WO2011115211A1 - Method for producing lithium manganese iron phosphate particulate powder, lithium manganese iron phosphate particulate powder and non-aqueous electrolyte secondary battery using that particulate powder - Google Patents

Abstract

Disclosed is a method for producing an olivine structured lithium manganese iron phosphate, LiMn_1-xFe_xPO₄ (0.05 ≤ x ≤ 0.5), particulate powder. The method is characterized by a first step for obtaining a water-based slurry by the neutralization reaction of a mixed solution of starting materials and a second step of carrying out heat treatment of the slurry obtained in the first step, having a production rate of 75 wt% or greater for the LiMn_1-xFe_xPO₄ (0.05 ≤ x ≤ 0.5) compound obtained and washing that compound after making the crystallite size 10 - 250 nm. The method is further characterized by a third step for obtaining a precursor powder with 3 - 40 wt% carbon content by adding an organic substance to the compound obtained in the second step and a fourth process for firing the precursor powder obtained in the third step. The particulate powder can be produced easily at low cost, and the charge and discharge capacity is large for secondary batteries. Also disclosed is a secondary battery using the method for producing the lithium manganese iron phosphate particulate powder, which has superior filling properties and repeated charging and discharging characteristics.

Description

Method for producing lithium manganese iron phosphate particle powder, lithium manganese iron phosphate particle powder, and nonaqueous electrolyte secondary battery using the particle powder

The present invention is a method for producing olivine-type lithium iron manganese phosphate particles that can be easily produced at low cost, and has a high energy density when used as a high-power secondary battery. Provided are lithium iron manganese oxide particles and a secondary battery using the same.

In recent years, electronic devices such as AV equipment and personal computers, and power tools such as electric tools have been rapidly becoming portable and cordless. As a power source for driving these, secondary batteries having a small size, light weight and high energy density have been developed. The demand is high. In consideration of the global environment, hybrid vehicles and electric vehicles have been developed and put into practical use, and the demand for secondary batteries with excellent output characteristics is increasing. Under such circumstances, a lithium ion secondary battery having advantages such as a large charge / discharge capacity and high safety has been attracting attention.

Recently, attention has been focused on 3.5V class olivine type structure LiFePO ₄ to 4.1V class LiMnPO ₄ as a positive electrode active material useful for a high energy density type lithium ion secondary battery. However, since LiMnPO ₄ is less liable to enter and exit Li than LiFePO ₄ , improvement of charge / discharge characteristics is required.

That is, LiMnPO ₄ having an olivine structure is composed of a strong phosphoric acid tetrahedral skeleton, an oxygen octahedron centered on manganese ions that contribute to redox, and lithium ions that are current carriers. Moreover, in order to supplement electron conductivity, there exists a tendency which coat | covers carbon on the particle | grain surface. Thus, it functions as an electrode of a secondary battery, and at the time of charge / discharge using Li as a negative electrode, it is said that it follows a two-phase reaction of the following formula due to the presence of a plateau region in charge / discharge characteristics indicated by capacity and voltage.

Charging: LiMnPO ₄ → MnPO ₄ + Li ⁺ + e ⁻
Discharge: MnPO ₄ + Li ⁺ + e ⁻ → LiMnPO ₄

By the way, there are various theories about the ease of Li in and out of the LiMnPO ₄ positive electrode and the stability of MnPO ₄ from which Li is desorbed. For this reason, it is considered that the crystal structure of the substance from which Li is eliminated by the charging reaction is stable, and it is necessary to reduce the change in the particle size before and after charging and discharging. One of them is a method in which Fe is dissolved in Mn sites (Non-Patent Documents 1 to 6).

LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) also has better charge / discharge characteristics at low current as the particle surface is coated with carbon. In addition, the smaller the crystallite size satisfies the above condition, the better the charge / discharge characteristics at a high current load. Moreover, as an electrode, in order to obtain a high molding density, each aggregate is formed so as to form a network of secondary particles that are appropriately aggregated and a conductive auxiliary agent such as carbon having a high graphitization rate. The state needs to be controlled. On the other hand, the positive electrode combined with a large amount of carbon is bulky, and there is a disadvantage that the substantial lithium ion density that can be filled per unit volume is lowered. Therefore, in order to secure charge / discharge capacity per unit volume, olivine-type lithium iron manganese phosphate coated with fine and moderate carbon was obtained and high density was obtained through a small amount of conductive auxiliary agent. There is a need to form aggregates.

In other words, as the positive electrode active material powder for non-aqueous electrolyte secondary batteries, lithium manganese iron phosphate particles having an olivine structure with a small change in particle size, low electrical resistance, and high filling property due to charge / discharge are used. It is required to produce by an industrial method with a small load.

Conventionally, various improvements have been made to improve various characteristics of olivine-type lithium iron manganese phosphate particles. For example, technology to reduce deterioration after charge / discharge cycle test (Patent Document 1), technology to add different metal elements to reduce electrical resistance (Patent Document 2), and to reduce electrical resistance by adding different metal elements and carbon coating Technology (Patent Document 3), technology synthesized by hydrothermal method (Patent Documents 4 to 6), and the like are known.

JP 2003-257429 A JP 2004-063270 A Special table 2008-130525 gazette JP 2007-035358 A JP 2007-119304 A JP 2008-066019 A

As a positive electrode active material for non-aqueous electrolyte secondary batteries, an inexpensive and efficient production method of lithium manganese iron phosphate particles having an olivine structure that satisfies the above-mentioned characteristics is currently the most demanded, but it is still established. It has not been.

That is, in the techniques described in Non-Patent Documents 1 to 6, LiMn _1-x Fe _x PO ₄ (0) having an olivine structure with little change in particle size due to charge / discharge, low electrical resistance, and high filling properties. .05 ≦ x ≦ 0.5) cannot be obtained industrially.

The technique described in Patent Document 1 is a technique for improving charge / discharge repetition characteristics when LiMn _1-x Fe _x PO ₄ particle powder having an olivine type structure is used as a positive electrode. There is no mention of collective control.

The technique described in Patent Document 2 is not a technique related to the composite of LiMnPO ₄ particle powder having an olivine structure and carbon.

Furthermore, the technique described in Patent Document 3 is a production method using a solid-phase reaction method, and since it has two heat treatments, it is difficult to say that the cost is low.

The hydrothermal methods described in Patent Documents 4 to 6 are: 1) a method in which lithium hydroxide is excessively charged to neutralize the raw material phosphoric acid or sulfate, and 2) the raw material phosphoric acid or transition metal-containing sulfate. From this method, a precipitate is produced, mixed with a lithium raw material, and charged at a Li: Mn + Fe: P = 1: 1: 1 mol ratio. In the case of 1), recovery of Li is required from the viewpoint of manufacturing cost, but it is considered a relatively difficult method. In the case of 2), there are almost no reported examples of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5), there is almost no mention of a precursor that performs hydrothermal treatment, and a description of controlling the aggregated particle size Was not found.

Therefore, the present invention establishes an industrial method of olivine-type lithium iron phosphate particles with a small olivine structure, which has a small change in particle size due to charge / discharge, low electrical resistance, and high packing properties, As a non-aqueous electrolyte secondary battery containing a high positive electrode active material, it is a technical subject to obtain a high capacity also in current load characteristics.

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

That is, the present invention relates to a method for producing olivine-type lithium manganese iron phosphate LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) particle powder, wherein the raw material is Li compound, Mn compound , Fe compound, P compound and sugar or organic acid, and the raw material charge ratio is 0.95 ≦ Li / (Mn + Fe) ≦ 2.0, 0.95 ≦ P / (Mn + Fe) ≦ 1.3 in terms of mol ratio Obtained in the first step and the first step of obtaining an aqueous slurry having a pH of 5.5 to 12.5 by a neutralization reaction of a mixed solution containing 1 to 20 mol% of sugar or organic acid with respect to (Mn + Fe) The slurry is hydrothermally treated at a reaction temperature of 120 to 220 ° C., and the resulting compound has a production rate of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) of 75 wt% or more, Size 10-250nm After that, the second step of washing the compound, the third step of obtaining a precursor powder by adding 3 to 40 wt% of organic substances to the compound obtained in the second step, the precursor powder obtained in the third step This is a method for producing olivine-type lithium iron manganese phosphate particles comprising a fourth step of firing at a temperature of 250 to 850 ° C. in an inert gas or reducing gas atmosphere having an oxygen concentration of 0.1% or less (this book) Invention 1).

Further, according to the present invention, in the first step, the median diameter of the aggregated particles in the slurry is 0.1 to 10 μm, and the crystal phase is (NH ₄ ) Mn _1-α Fe _α PO ₄ (0 ≦ α < 1) or a manufacturing method according to the first aspect of the present invention for obtaining an aqueous slurry containing aggregated particles satisfying HMn _1-β Fe _β PO ₄ (0 ≦ β <1) (Invention 2).

Moreover, this invention is the manufacturing method of this invention 1 or 2 whose saccharide | sugar or organic acid used in said 1st process is at least 1 sort (s) among sucrose, ascorbic acid, and a citric acid (this invention 3). ).

Further, the present invention is the production method according to any one of the present inventions 1 to 3, wherein in the second step, washing is performed so that the sulfur content in the compound is 0.1 wt% or less (Invention 4). .

Further, the present invention is the production method according to any one of the present inventions 1 to 4, wherein in the third step, the organic substance to be added is at least one of carbon black, an oil and fat compound, a sugar compound, and a synthetic resin. (Invention 5).

The present invention also relates to olivine type lithium manganese iron phosphate LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) particle powder, wherein the content of lithium and phosphorus is in a molar ratio. 0.9 ≦ Li / (Mn + Fe) ≦ 1.2, 0.9 ≦ P / (Mn + Fe) ≦ 1.2, the BET specific surface area is 6 to 70 m ² / g, and the carbon content is 0.5 8 wt%, the sulfur content is 0.08 wt% or less, and the amount of the crystalline phase LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) of the olivine type structure is 95 wt% or more. The crystallite size is 25 to 300 nm, the median diameter of the aggregated particles is 0.3 to 20 μm, and the electrical resistivity of the powder is 1 to 1.0 × 10 ⁶ Ω · cm. This is an olivine-type lithium iron manganese phosphate powder (this Invention 6).

The present invention also relates to lithium iron manganese phosphate particles having an olivine structure according to the present invention 6, wherein the lithium and phosphorus contents satisfy Li ≧ P (the present invention 7).

The present invention also relates to lithium iron manganese phosphate particles having an olivine structure according to the present invention 6 or 7, wherein the unit cell volume V _UC has the relationship represented by the following formula (1) (the present invention 8).
V _UC (Å ³ ) <11.4 × (1-x) +291.21 (1)

Further, the present invention is a non-aqueous electrolyte secondary battery produced using the olivine-type lithium manganese iron phosphate particles according to any one of the present inventions 6 to 8 (Invention 9).

The method for producing olivine-type lithium iron manganese phosphate particles according to the present invention is low-cost and can be produced efficiently from almost equal amounts of raw materials. Is preferred.

In addition, the lithium olivine manganese phosphate particles having an olivine structure according to the present invention have little change in particle size due to charge / discharge, low electrical resistance, and high filling properties, and are used for non-aqueous electrolyte secondary batteries. Suitable as a positive electrode active material.

Further, the secondary battery using the olivine-type lithium manganese iron phosphate particles having the olivine structure as the positive electrode active material according to the present invention has a high capacity in the current load characteristics and can sufficiently withstand repeated charge and discharge.

2 is a secondary electron image of the olivine-type lithium manganese iron phosphate particles obtained in Example 1 by a scanning electron microscope. It is the discharge characteristic which made the positive electrode the olivine type structure lithium iron iron phosphate particle powder obtained in Example 1, and evaluated it by the coin cell. It is a secondary electron image by the scanning electron microscope of the lithium iron manganese phosphate particle powder of the olivine type structure obtained in Comparative Example 4. It is a secondary electron image by the scanning electron microscope of the particle powder obtained by chemically oxidizing the lithium iron manganese phosphate particle powder of the olivine type structure obtained in Comparative Example 4. It is a Rietveld analysis result of the X-ray-diffraction pattern of the particle powder obtained by chemically oxidizing the lithium iron manganese phosphate particle powder of the olivine type structure obtained in Comparative Example 4.

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

First, a method for producing olivine-type lithium iron manganese phosphate according to the present invention will be described.

The method for producing olivine-type lithium manganese iron phosphate LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) particle powder according to the present invention includes a Li compound, a Mn compound, an Fe compound, Using a P compound and a sugar or an organic acid, the raw material charge ratio is 0.95 ≦ Li / (Mn + Fe) ≦ 2.0, 0.95 ≦ P / (Mn + Fe) ≦ 1.3 in terms of mol ratio, and (Mn + Fe) The first step of obtaining an aqueous slurry having a pH of 5.5 to 12.5 by the neutralization reaction of a mixed solution containing 1 to 20 mol% of sugar or organic acid with respect to the reaction temperature, the slurry obtained in the first step is the reaction temperature Hydrothermal treatment is performed at 120 to 220 ° C., and the resulting compound has a production rate of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) of 75 wt% or more, and a crystallite size of 10 to After 250 nm, The second step of washing the compound, the third step of obtaining a precursor powder by adding 3 to 40 wt% of organic substances to the compound obtained in the second step, and the oxygen concentration of the precursor powder obtained in the third step of 0. It is characterized by comprising a fourth step of baking at a temperature of 250 to 850 ° C. in an inert gas or reducing gas atmosphere of 1% or less.

The raw materials used in the first step are preferably LiOH and Li ₃ PO ₄ as the Li compound, MnSO ₄ and MnCO ₃ as the Mn compound, FeSO ₄ and FeCO ₃ as the Fe compound, and P compound as the P compound. H ₃ PO ₄ , (NH ₄ ) H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ , NaH ₂ PO ₄ , Na ₂ HPO ₄ , and Na ₃ PO ₄ are preferred.

The Li compound, Mn compound, Fe compound, and P compound in the first step have a raw material charge ratio of 0.95 ≦ Li / (Mn + Fe) ≦ 2.0 and 0.95 ≦ P / (Mn + Fe) ≦ 1. 3 to be mixed. When the raw material charge ratio is outside the above range, the target lithium iron manganese phosphate cannot be obtained. More preferably, the molar ratio is 0.98 ≦ Li / (Mn + Fe) ≦ 1.8 and 0.98 ≦ P / (Mn + Fe) ≦ 1.2.

The sugar or organic acid used in the first step is preferably sucrose, ascorbic acid, or citric acid. The addition amount of sugar or organic acid is 1 to 20 mol%, more preferably 1.5 to 18 mol%, based on (Mn + Fe). The added sugar or organic acid works as a transition metal reducing agent, and after hydrothermal reaction. The production rate of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) is increased, and the primary particle diameter of the product is refined.

As the alkali source used in the first step, LiOH, NaOH, Na ₂ CO ₃ , NH ₃ , urea, ethanolamine or the like is used.

The aqueous slurry in the first step has a pH of 5.5 in order to increase the production rate of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) of the compound obtained by the hydrothermal treatment in the second step. Must be ~ 12.5.

The median diameter of the aggregated particles in the slurry in the first step is preferably 0.1 to 10 μm.

In the slurry in the first step, the crystal phase of the aggregated particles in the slurry is (NH ₄ ) Mn _1-α Fe _α PO ₄ (0 ≦ α <1) or HMn _1-β Fe _β PO ₄ (0 ≦ β <1). It is preferable that the agglomerated particles are included. When one of the two phases is not included, the target lithium manganese iron phosphate cannot be obtained.

The agglomerated particles having the median diameter and the crystal phase can be obtained by mixing raw materials under conditions where crystal nuclei are generated and grown (generation of a large number of crystal nuclei) or by pulverization of the product. Examples of the apparatus used for pulverization include a ball mill and a medium stirring mill.

The hydrothermal treatment in the second step is preferably performed at 120 to 220 ° C. The hydrothermal treatment time is preferably 1 to 10 hours.

In the compound obtained by performing the hydrothermal treatment in the second step, the production rate of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) is 75 wt% or more. When the production rate is less than 75 wt%, the production rate of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) remains low even after the subsequent steps. A more preferable production rate is 80 wt% or more. The crystallite size of the obtained compound based on LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) is 10 to 250 nm. A compound having a crystallite size of less than 10 nm is industrially difficult to produce, and a compound having a crystallite size of more than 250 nm cannot obtain good battery characteristics. A more preferable crystallite size is 30 to 150 nm. The hydrothermal treatment in the second step needs to be performed by appropriately selecting the treatment temperature and the treatment time so as to satisfy the above generation rate and crystallite size. If the hydrothermal treatment temperature is low and the treatment time is short, the above-mentioned production rate may not be reached, or the crystallite size may not be reached, and if the hydrothermal treatment temperature is high and the treatment time is long, the above crystals May exceed child size.

The compound obtained by the hydrothermal treatment in the second step is subjected to filtration washing or decantation washing in order to remove impurity sulfate ions and control the composition ratio. Examples of the apparatus used for cleaning include a press filter and a filter thickener.

The washing of the compound obtained by the hydrothermal treatment in the second step is preferably performed so that the sulfur content in the compound is 0.1 wt% or less. Washing is sufficient if sulfur in the compound can be sufficiently removed, and usually washing with water may be performed.

In order to form a lithium manganese iron phosphate solid solution, it is preferable to adjust the composition ratio of the main component elements in the third step. If necessary, Li compound, Mn compound, Fe compound, and P compound are added to the compound obtained in the second step, and the composition ratio of main component elements is Li: (Mn + Fe): P = 0.90: 1: 0. It is preferable to adjust to a range of 90 to 1.20: 1: 1.20 (mol ratio).

For the adjustment of the composition ratio of the main component elements, lithium compounds such as LiOH and Li ₂ CO ₃ are used for adjusting Li, manganese compounds such as MnCO ₃ and MnC ₂ O ₄ are used for adjusting Mn, and FeCO ₃ and FeC are used for adjusting Fe. It is preferable to use an iron compound such as ₂ O _{4 and} a PO ₄ -containing compound such as H ₃ PO ₄ , (NH ₄ ) H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ for adjusting P.

Also, in order to form a fine lithium iron manganese phosphate solid solution coated with carbon, 3 to 40 wt% of an organic substance is added in the third step to obtain a precursor powder. At that time, it is necessary to reduce the primary particle size of the precursor powder and to uniformly mix with the organic matter. Examples of the apparatus used for mixing include a Henschel mixer, a raking machine, a high speed mixer, a medium stirring mill, and the like.

The organic substance to be added is preferably at least one of carbon black, an oil and fat compound, a sugar compound, and a synthetic resin.

In order to coat the surface of fine lithium iron manganese phosphate particles with carbon and to control the aggregated particle diameter, the organic substance added is preferably at least one of an oil and fat compound, a sugar compound, and a synthetic resin.

Further, when carbon black having high conductivity is used as the organic substance to be added, firing at a low temperature is possible in the fourth step. By using carbon black, the resulting compacted compact of olivine-type lithium manganese iron phosphate particles even at low temperatures such as 400 to 500 ° C. has an electrical resistivity of 1 to 1.0 × 10 ⁶ Ω · cm. Satisfying and high performance secondary battery characteristics.

Examples of the oil and fat compound include stearic acid and oleic acid, examples of the sugar compound include sucrose and dextrin, and examples of the synthetic resin include polyethylene, polypropylene, and polyvinyl alcohol (PVA).

Further, examples of carbon black include acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) and ketjen black (manufactured by Lion Corporation).

In addition, it is preferable to adjust the aggregate particle diameter of the precursor powder to 0.3 to 30 μm by binding particles with an organic substance added in the third step. Preferred binders include polyvinyl alcohol (PVA), polyvinyl butyral, starch, carboxymethyl cellulose and the like.

The precursor powder obtained in the third step is fired at a temperature of 250 to 850 ° C. in an inert gas or reducing gas atmosphere having an oxygen concentration of 0.1% or less. As the inert gas, N ₂ , Ar, H ₂ O, CO ₂ or a mixed gas thereof is used. As the reducing gas, H ₂ , CO, or a mixed gas of these gases and the inert gas is used. Examples of the apparatus used for firing include a gas flow type box muffle furnace, a gas flow type rotary furnace, and a fluidized heat treatment furnace.

By firing in an atmosphere with an oxygen concentration of 0.1% or less, a small amount of Fe ³⁺ contained in the Fe raw material is changed to Fe ²⁺ by the added organic substance or reducing gas, and LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) is generated. For the production of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5), the calcination temperature may be 250 ° C. or higher, but the reaction of unreacted substances is completed, and the added organic matter In order to form a graphite phase having a high electron conductivity from 350 to 850 ° C., it is preferably calcined at 350 to 850 ° C., more preferably at 400 to 750 ° C. for 1 to 10 hours.

The lithium iron manganese phosphate particles according to the present invention can produce LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) after hydrothermal treatment by adjusting an appropriate precursor slurry. The rate can be increased. Thereafter, the mixture is uniformly mixed with an organic substance and further baked, whereby the production rate of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) is high, and fine manganese phosphate sufficiently covered with carbon Iron lithium particle powder can be obtained.

Next, the olivine type lithium manganese phosphate LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) particle powder for non-aqueous electrolyte secondary battery according to the present invention will be described. The lithium iron manganese phosphate particles according to the present invention are preferably produced by the production method according to the present invention 1 described above.

In the lithium iron manganese phosphate particles according to the present invention, the content of lithium and phosphorus is 0.9 ≦ Li / (Mn + Fe) ≦ 1.2 and 0.9 ≦ P / (Mn + Fe) ≦ 1.2 in terms of mol ratio. It is. When the content of lithium and phosphorus is outside the above range, a heterogeneous phase is likely to be formed, and in some cases, grain growth is promoted and lithium manganese iron phosphate particles having high battery characteristics cannot be obtained. Preferable lithium and phosphorus contents are 0.98 ≦ Li / (Mn + Fe) ≦ 1.05, 0.98 ≦ P / (Mn + Fe) ≦ 1.05, and more preferably 1 ≦ Li / (Mn + Fe) in molar ratio. ) ≦ 1.05, 1 ≦ P / (Mn + Fe) ≦ 1.05.

Furthermore, the lithium manganese iron particle powder according to the present invention preferably has a lithium and phosphorus content of Li ≧ P.

The BET specific surface area of the lithium iron manganese phosphate particles according to the present invention is 6 to 70 m ² / g. When the BET specific surface area is less than 6 m ² / g, the movement of Li ions in the lithium iron manganese phosphate particle powder is slow, so that it is difficult to take out the current. When exceeding 70 m < ² > / g, since the packing density of a positive electrode falls and the reactivity with electrolyte solution increases, it is unpreferable. A preferred BET specific surface area is 10 to 65 m ² / g, more preferably 15 to 60 m ² / g.

The carbon content of the lithium iron manganese phosphate particles according to the present invention is 0.5 to 8.0 wt%. When the carbon content is less than 0.5 wt%, the particle growth during the heat treatment cannot be suppressed, and the electric resistance of the obtained powder is increased, which deteriorates the charge / discharge characteristics of the secondary battery. On the other hand, when the carbon content exceeds 8.0 wt%, the packing density of the positive electrode is lowered, and the energy density per volume of the secondary battery is reduced. A more preferable carbon content is 1.0 to 6.0 wt%.

The lithium iron manganese phosphate particles according to the present invention have an impurity sulfur content of 0.08 wt% or less, and good storage characteristics can be obtained in a nonaqueous electrolyte secondary battery. When the sulfur content exceeds 0.08 wt%, impurities such as lithium sulfate are formed, and these impurities undergo a decomposition reaction during charge and discharge, and the reaction with the electrolyte during high-temperature storage is promoted, and after storage Resistance rises intensely. A more preferable sulfur content is 500 ppm or less.

In the lithium iron manganese phosphate particles according to the present invention, the crystal phase of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) having an olivine structure is 95 wt% or more. When Li ₃ PO ₄ is detected as the impurity crystal phase, LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) particles obtained after firing may be fine and the discharge capacity may be high. However, since Li ₃ PO ₄ itself does not contribute to charging and discharging, it is desirable that it be less than 5 wt%.

The crystallite size of the lithium iron manganese phosphate particles according to the present invention is 25 to 300 nm. It is extremely difficult to mass-produce a powder having a crystallite size of less than 25 nm while satisfying other powder characteristics by the production method of the present invention, and Li moves inside the particle at a crystallite size exceeding 300 nm. Time is required and the current load characteristics of the secondary battery are deteriorated. The preferred crystallite size is 30 nm to 200 nm, more preferably 40 nm to 150 nm.

The median diameter of the aggregated particles of the lithium iron manganese phosphate particles according to the present invention is 0.3 to 30 μm. When the median diameter is less than 0.3 μm, the positive electrode packing density is decreased and the reactivity with the electrolytic solution is increased. On the other hand, when the median diameter exceeds 30 μm, it is too large for the electrode film thickness and it is extremely difficult to form a sheet. A preferable median diameter of the aggregated particles is 0.5 to 15 μm.

The density of the compression molded body of the lithium iron manganese phosphate particles according to the present invention is preferably 1.8 g / cc or more. The true density of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) is 3.6 g / cc, and the closer to the true density, the better the filling property. Therefore, a preferable compression molding density is 2.0 g / cc or more exceeding 50% of the true density. On the other hand, it is extremely difficult to mass-produce a powder having a compression molded body density of 2.8 g / cc or more while satisfying other powder characteristics by the production method of the present invention. The lithium manganese iron phosphate particle powder according to the present invention is considered to have a high compression-molded body density because the amount of remaining carbon is small and primary particles are appropriately aggregated.

The powder electrical resistivity of the lithium iron manganese phosphate particles according to the present invention is 1 to 1.0 × 10 ⁶ Ω · cm. By combining carbon with lithium manganese iron phosphate having a powder electrical resistivity of about 1.0 × 10 ⁸ Ω · cm, the powder electrical resistivity could be reduced. The powder electrical resistivity is preferably 1 to 5.0 × 10 ⁵ Ω · cm, more preferably 5 to 1.0 × 10 ⁵ Ω · cm.

The unit cell volume V _UC of the lithium iron manganese phosphate particles according to the present invention is preferably in the relationship of formula (1).
V _UC (Å ³ ) <11.4 × (1-x) +291.21 (1)

In general, it is well known that the lattice constant and the unit cell volume decrease linearly with the increase of the value of _{x in} LiMn _1-x Fe _x PO _{4 having} an olivine structure, and follow Vegard's law. The unit cell volume of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) having an olivine structure inferred from the linearity of the Vegard rule is 10.9 × (1-x) +291.36 Met. The closer to the unit cell volume, the transition metal substitution to the Li site and the loss of P and O are reduced. When the volume is smaller than the unit cell volume, Li is substituted to the transition metal site, and the theoretical capacity as an electrode is reduced. I think it will increase.

According to the heat treatment of a precursor having a composition ratio deviated from the stoichiometric ratio of LiMn _1-x Fe _x PO ₄ having an olivine structure, the present inventors have made LiMn _1-x Fe _x PO ₄ ( It was confirmed that an impurity crystal phase that exists more stably than 0.05 ≦ x ≦ 0.5) tends to be generated. In addition, although the composition ratio of Li, Mn, Fe, and P is slight and a olivine-type LiMn _1-x Fe _x PO ₄ single crystal phase is formed, different lattice constants are obtained. In some cases, the unit cell volume is more than the above formula (1). In that case, it is assumed that the transition metal substitution to the Li site and the loss of P and O occur, and the battery characteristics deteriorate.

Next, a nonaqueous electrolyte secondary battery using the olivine-type lithium manganese iron phosphate particles according to the present invention as a positive electrode active material will be described.

When a positive electrode sheet is produced using the lithium iron manganese phosphate particles according to the present invention as a positive electrode active material, 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. As the solvent, for example, N-methyl-pyrrolidone is used, and the positive electrode active material sieved to 45 to 105 μm or less and the slurry containing the additive are kneaded until they become honey. The obtained slurry is applied onto the current collector with a doctor blade having a groove of 25 μm to 500 μm. The coating speed is about 60 cm / sec, and an Al foil of about 20 μm is usually used as a current collector. In order to remove the solvent and soften the binder, drying is performed at 80 to 180 ° C. in a non-oxidizing atmosphere of Fe ²⁺ . The sheet is subjected to a calender roll treatment so as to have a pressure of 1 to 3 t / cm ² . In the step of forming the sheet, an oxidation reaction of Fe ²⁺ to Fe ³⁺ occurs even at room temperature.

In the positive electrode sheet of the present invention, the density of the compression molded body of the positive electrode active material is as high as 1.8 g / cc or more, and the electrical resistivity of the compression molded body of the positive electrode active material is 1 to 1.0 × 10 ⁶ Ω.・ Because it is as low as cm, the amount of carbon added during sheet preparation can be suppressed, and since the BET specific surface area of the positive electrode active material is as low as 6 to 70 m ² / g, the amount of binder added can be suppressed, resulting in density A high positive electrode sheet is obtained.

As the negative electrode active material, lithium metal, lithium / aluminum alloy, lithium / tin alloy, graphite or the like can be used, and the negative electrode sheet is produced by the same doctor blade method or metal rolling as the positive electrode.

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.

<Action>
The olivine-type lithium iron manganese phosphate LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) particle powder according to the present invention is produced by hydrothermal reaction and firing, and is low in cost and in a small environment Can be manufactured with load.

That is, the present invention is the manufacturing method of _{LiMn 1-x Fe} x PO 4 of olivine (0.05 ≦ x ≦ 0.5), LiMn 1-x Fe x PO 4 by hydrothermal reaction (0.05 ≦ x ≦ 0.5) is produced at a high production rate, then uniformly mixed with an organic substance to control the aggregated particle size, and fired under conditions of an inert or reducing atmosphere, and is finely coated with carbon. In addition, it is possible to obtain a particle powder having a high filling property.

In addition, since the lithium iron manganese phosphate particles produced by the production method of the present invention controlled the carbon coating and the aggregated particle size, the nonaqueous electrolyte secondary battery using this as a positive electrode active material also has a current load characteristic. The present inventor estimates that a high capacity can be obtained and that it can sufficiently withstand repeated charge and discharge.

The non-aqueous electrolyte secondary battery using the olivine-type lithium iron manganese phosphate particles according to the present invention as a positive electrode active material has a discharge capacity at 115 Ch / g at room temperature (25 ° C.) of 115 mAh / g or more. The discharge capacity at 1 C at 95 ° C. is at least 95 mAh / g, and the discharge capacity at 5 C at room temperature is at least 80 mAh / g.

A typical embodiment of the present invention is as follows.

The Li and P concentrations of the lithium and phosphorus-containing main raw materials were measured by neutralization titration using a pH meter and hydrochloric acid or NaOH reagent. The Fe concentration of the iron raw material was quantified by titration (JIS K5109), and the Mn concentration of the manganese raw material was also quantified by titration (Analytical Chemistry Handbook, edited by the Japan Analytical Chemical Society). Based on these analysis results, the reaction concentration and the raw material charge ratio were determined.

Particle size of the aggregated particles in the slurry in the first step, using a laser diffraction scattering type particle size distribution meter HELOS ((KK) Japan Laser) were measured median diameter D ₅₀ by a wet method.

The crystal phase of the aggregated particles in the slurry in the first step was obtained by filtering the aggregated particles in the slurry, and using Cu-Kα, a wet cake using an X-ray diffractometer RINT-2500 [manufactured by Rigaku Corporation]. Measurement was performed under conditions of 40 kV and 300 mA, and the crystal phase was identified.

Compound obtained by hydrothermal treatment in the second step, crystal phase and crystallite size of lithium iron phosphate particles in the present invention, and formation of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) The rate was calculated by Rietveld analysis of an X-ray diffraction pattern measured using an X-ray diffractometer RINT-2500 [manufactured by Rigaku Corporation]. The X-ray diffraction pattern was measured in steps of 0.02 ° and 1.0 ° / min in the range of 2θ of 15 to 90 ° so that the count number of the maximum peak intensity was 8000 to 15000. Rietan 2000 was used as the Rietveld analysis program. At that time, assuming that there is no anisotropic broadening of the crystallite, the TCH pseudo-void function is used as the profile function, the method such as Finger is used for asymmetry of the function, and the reliability factor S value is 2.0. Analyzed to cut.

<References>
F. Izumi and T. Ikeda, Mater. Sci. Forum, 2000, Vol. 198, p. 321-324.

The unit cell volume of the lithium iron manganese phosphate particles having the olivine structure (space group Pnma) according to the present invention was calculated from the product of the lattice constants a, b and c calculated by the Rietveld analysis.

In the third step, the composition ratio of the compound powder after adjusting the composition ratio of the compound obtained by the hydrothermal treatment in the second step and the lithium manganese iron phosphate particle powder according to the present invention is determined by the emission plasma analyzer ICAP-6500 [Thermo [Fischer Scientific]. The sample was dissolved in an acid solution at 200 ° C. using an autoclave.

The specific surface area of the lithium iron manganese phosphate particles according to the present invention was measured using MONOSORB [manufactured by Yuasa Ionics Co., Ltd.] after drying and deaeration of the sample under nitrogen gas at 120 ° C. for 45 minutes.

Particle size of the manganese phosphate lithium iron particles of agglomerated particles according to the present invention, using a HELOS [(KK) Japan Laser is a laser diffraction scattering type particle size distribution meter, measuring the median diameter D ₅₀ by a dry process did.

Carbon and sulfur amounts were quantified by burning them in an oxygen stream in a combustion furnace using EMIA-820 [manufactured by Horiba Ltd.].

The density of the compression molded body of the lithium iron manganese phosphate particles according to the present invention was calculated from the weight and volume of the compression molded body when compacted to 1.5 t / cm ² with a 13 mmφ jig. Moreover, the powder electrical resistivity was measured by the two-terminal method using the compression molded body.

As an evaluation of the change of the particle size accompanying charging / discharging of the lithium iron manganese phosphate particles according to the present invention, a pseudo charged state in which Li is desorbed by chemical oxidation with NO ₂ BF ₄ is created, and the primary particle size before and after the chemical oxidation The rate of change was calculated.

In an acetonitrile solvent, NO ₂ BF ₄ having a molar number twice that of Li in the powder iron manganese phosphate is added to the powder of lithium manganese phosphate, left to stand for chemical oxidation, washed with acetonitrile and washed with Li. A particle powder with all removed was obtained. For the particle powder before and after chemical oxidation, the primary particle diameter was measured by SEM photographs obtained with a scanning electron microscope (SEM) of Hitachi S-4800 type, and the change rate of the primary particle diameter before and after chemical oxidation was calculated.

The secondary battery characteristics of the CR2032-type coin cell were evaluated using the lithium iron manganese phosphate particles having an olivine structure according to the present invention.

Acetylene black as a conductive material and polyvinylidene fluoride having a polymerization degree of 540,000 (manufactured by Aldrich) dissolved in N-methylpyrrolidone (manufactured by Kanto Chemical Co., Ltd.) as a binder are mixed, and positive electrode active material: acetylene black: PVDF = 88 4: The positive electrode material slurry was adjusted to 8 wt%, applied onto an Al current collector with a doctor blade, dried in air at 120 ° C. for 10 minutes, and the dried sheet was pressurized to 3 t / cm ² to form a positive electrode A sheet was produced.

Positive electrode sheet punched to 2 cm ² , 0.15 mm Li negative electrode punched to 17 mmφ, separator (Celguard # 2400) to 19 mmφ, EC and DEC (volume ratio 3: 7) in which 1 mol / l LiPF ₆ was dissolved were mixed A CR22032 type coin cell (manufactured by Hosen Co., Ltd.) was prepared using an electrolytic solution (manufactured by Kishida Chemical).

The charge / discharge characteristics of the non-aqueous electrolyte secondary battery using the olivine type lithium iron manganese phosphate particles according to the present invention as the positive electrode active material were measured by measuring the discharge capacity at C / 10, 1C, and 5C at room temperature. And evaluated. Here, C / 10 is 10 hours, 1C is 1 hour, 5C is 1/5 hour, and the theoretical capacity of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5). The current value is fixed so that a current of 170 mAh / g flows. A higher C coefficient means higher current load characteristics. The voltage range during charging and discharging is not particularly limited, but in the present invention, the voltage range was 2.0 to 4.5V.

[Example 1]
A solution of MnSO _4, H ₃ PO ₄ , and NH ₄ OH was mixed, and NH ₄ MnPO ₄ was precipitated by a neutralization reaction at room temperature. After the precipitate was filtered off and washed with pure water, a solution of LiOH.H ₂ O, FeSO ₄ , H ₃ PO ₄ , and ascorbic acid was added, and the aqueous slurry adjusted to the raw material charge ratio shown in Table 1 Got.

The slurry was mixed with a ball mill, and the aggregated particles were pulverized to adjust the particle size. The adjusted slurry had a pH of 11, the median diameter of the aggregated particles was D ₅₀ = 5.0 μm, and the main crystal phase of the aggregated particles after filtration was NH ₄ MnPO ₄ (first step).

The slurry was hydrothermally treated at 180 ° C. for 3 hours, and the resulting compound was filtered off, washed with pure water, and dried at 70 ° C. overnight. From the Rietveld analysis of the XRD pattern, the obtained dry powder has a production rate of LiMn _1-x Fe _x PO ₄ of 95% and 5 wt% of Li ₃ PO ₄ as an impurity crystal phase other than the olivine structure. confirmed. The crystallite size was 70 nm according to Scherrer's equation. Further, the content of impurity sulfur in the dry powder was 0.1 wt% or less (second step).

In order to adjust the composition ratio, fine (NH ₄ ) H ₂ PO ₄ was added to the dry powder. The composition of the powder after adjustment was analyzed using ICP, and was Li: Mn: Fe: P = 1.01: 0.80: 0.20: 1.00 (mol ratio).

10 wt% sucrose was mixed in the agate mortar with respect to the obtained dry powder, a small amount of pure water was added, and the aggregated particle diameter was adjusted with a Henschel mixer to obtain a precursor powder (third step).

The precursor powder obtained in the third step was put in an alumina crucible and baked in a nitrogen atmosphere at 650 ° C. for 5 hours. The temperature increase rate was 200 ° C./hr, and the N ₂ gas flow rate was 1 L / min (fourth step).

The obtained powder was lithium iron manganese phosphate particles having an olivine structure, and the composition ratio thereof was the same as the composition ratio of Li, Mn, Fe, and P adjusted in the third step.

FIG. 1 shows an SEM photograph (secondary electron image) of the olivine-type lithium iron manganese phosphate particles obtained. Table 1 shows the manufacturing conditions of the first step and the properties of the obtained slurry, Table 2 shows the characteristics of the powder in the second step and the manufacturing conditions of the third step, and Table 3 shows the obtained lithium iron manganese phosphate. The powder characteristics of the particle powder are shown in Table 4 and FIG. 2 as the battery characteristics evaluated by a coin cell using the obtained lithium iron manganese phosphate particle powder as a positive electrode.
Further, the change rate of the primary particle size before and after the removal of Li by chemical oxidation was about 10%.

[Example 2]
The same processing as in Example 1 was performed except that the raw material charging ratio was changed as shown in Table 1.

[Example 3]
A solution of Fe ₃ (PO ₄ ) ₂ .8H ₂ O, Li ₃ PO ₄ and LiOH.H ₂ O was added to NH ₄ MnPO ₄ obtained in the same manner as in Example 1, and the raw material charging ratios are as shown in Table 1. An aqueous slurry was obtained in the same manner as in Example 1 except that Thereafter, PVA was added as an organic substance in the third step to the slurry after the hydrothermal reaction, and the same treatment as in Example 1 was performed except that the slurry was evaporated to dryness.

[Example 4]
A solution of MnSO ₄ , FeSO ₄ , H ₃ PO ₄ , NH ₄ OH was mixed, and NH ₄ Mn _0.7 Fe _0.3 PO ₄ was precipitated by a neutralization reaction at room temperature. The obtained precipitate was separated by filtration and washed with pure water, and then LiOH.H ₂ O, H ₃ PO ₄ and sucrose were added to obtain an aqueous slurry adjusted to the raw material charging ratio shown in Table 1. Thereafter, the same treatment as in Example 1 was carried out except that 15 wt% of polyethylene and stearic acid were used as organic substances in the third step.

[Example 5]
A solution of MnSO ₄ and Na ₂ CO ₃ was mixed, and MnCO ₃ was precipitated by a neutralization reaction at room temperature. The obtained precipitate was separated by filtration and washed with pure water, and then H ₃ PO ₄ was added to precipitate HMnPO ₄ . Thereafter, the same processing as in Example 1 was performed except that the raw material charging ratio was changed as shown in Table 1.

[Example 6]
A solution of MnSO ₄ , FeSO ₄ , and Na ₂ CO ₃ was mixed, and HMn _0.9 Fe _0.1 CO ₃ was precipitated by a neutralization reaction at room temperature. The resulting precipitate was filtered and washed with pure water, and then a solution of H ₃ PO ₄ was added to precipitate HMn _0.9 Fe _0.1 PO ₄ . Thereafter, the same processing as in Example 1 was performed except that the raw material charging ratio was changed as shown in Table 1.

[Example 7]
The raw material charging ratio was changed as shown in Table 1, and treatment was performed in the same manner as in Example 1 except that 20 wt% of sucrose and carbon black were used as organic substances in the third step.

[Comparative Example 1]
A solution of MnSO _4, H ₃ PO ₄ , and NH ₄ OH was mixed, and NH ₄ MnPO ₄ was precipitated by a neutralization reaction at room temperature. The obtained precipitate was separated by filtration and washed with pure water, and then a solution of LiOH.H ₂ O and ascorbic acid was added to obtain an aqueous slurry adjusted to the raw material charge ratio shown in Table 1. The same treatment as in Example 1 was performed except that the particle size of the aggregated particles of the slurry was not adjusted.

In the first step, the agglomerated particles of the slurry were not pulverized, so the median diameter D ₅₀ of the agglomerated particles was as large as 16 μm, and the yield of LiMnPO ₄ having a olivine structure of the compound obtained after hydrothermal treatment was as low as 71 wt%. It was. Even in the lithium manganese iron phosphate particles powder obtained by firing, 7 wt% of Li ₃ PO ₄ which is an impurity crystal phase was present, and the battery characteristics deteriorated.

[Comparative Example 2]
An aqueous system adjusted to the raw material charge ratio shown in Table 1, including a precipitate obtained by mixing a solution of MnSO _4, FeSO ₄ , H ₃ PO ₄ , and LiOH · H ₂ O and neutralizing reaction at room temperature A slurry was obtained. The slurry was mixed with a ball mill, the aggregated particles were pulverized to adjust the particle size, then hydrothermally treated at 180 ° C. for 3 hours, the resulting precipitate was filtered, washed with pure water, and dried at 70 ° C. overnight. . Thereafter, the same processing as in Example 1 was performed. The crystallite size of the obtained dry powder was as large as 260 nm, and impurity sulfur in the dry powder was 0.12 wt%. The lithium manganese iron phosphate particle powder obtained by firing had a large sulfur content and crystallite size, and the battery characteristics were poor.

[Comparative Example 3]
The same process as in Example 2 was performed except that the amount of sucrose, which is an organic substance, was changed to 1 wt% in the third step of Example 2. The lithium manganese iron phosphate particles obtained by firing were coarse particles, had high electric resistance, and had poor battery characteristics.

[Comparative Example 4]
Li ₂ CO ₃ , MnCO ₃ , (NH ₄ ) H ₂ PO ₄ are mixed so that the ratio of Li, Mn, and P is 1: 1: 1, and a mixed solvent composed of ethanol and water to which PVA is further added. After pulverizing and mixing with a ball mill, the obtained compound was separated by filtration and fired in air at 700 ° C. for 2 hours to obtain lithium iron manganese phosphate particles. The obtained lithium iron manganese phosphate particles were coarse particles, had high electric resistance, and had poor battery characteristics.

FIG. 3 shows an SEM photograph of the obtained lithium iron manganese phosphate particle powder, FIG. 4 shows an SEM photograph when Li is eliminated by chemical oxidation, and FIG. 5 shows a Rietveld analysis result of the XRD pattern. It was confirmed that LiMnPO ₄ was changed to fine MnPO ₄ by chemical oxidation.

[Comparative Example 5]
An aqueous slurry was obtained in the same manner as in Example 3. Without performing the hydrothermal reaction in the second step, the precipitate in the slurry was separated by filtration, washed with pure water, and dried at 70 ° C. overnight. Thereafter, the same processing as in Example 1 was performed. The lithium manganese iron phosphate particle powder obtained by firing contained a large amount of impurity crystal phase Li ₃ PO ₄ , and the battery characteristics were poor.

The non-aqueous electrolyte secondary battery using the olivine type lithium iron manganese phosphate particles according to the present invention as a positive electrode active material has a discharge capacity of 115 mAh / g or more at C / 10 at room temperature and 1 C at room temperature. The discharge capacity was 95 mAh / g or more, and the discharge capacity at 5 C at room temperature was 80 mAh / g or more.

Further, in order to create a pseudo-charged state, chemical oxidation is performed with NO ₂ BF _4, which is half the number of moles of Li, and when Li is desorbed, the primary particle diameter tends to be 50 to 100 nm. The larger the particle size is 200 nm or more, the higher the change rate of the primary particle size before and after chemical oxidation.

[Examples 8 to 15]
The precursor powder obtained in the second step was changed to Li ₂ CO ₃ , MnCO ₃ , FeC ₂ O ₄ , (NH ₄ ) in the same manner as in Example 1 except that the raw material charging ratio was changed as shown in Table 5. Fine powders of H ₂ PO ₄ and (NH ₄ ) ₂ HPO ₄ were added as necessary and mixed by a ball mill, and the composition ratios of Li, Mn, Fe, and P were adjusted as shown in Table 5. Thereafter, the same processing as in Example 1 was performed.

The main component of the obtained powder was lithium iron manganese phosphate particles having an olivine structure, and the composition ratio was the same as the composition ratio of Li, Mn, Fe, and P adjusted in the third step.

Table 5 shows the manufacturing conditions of the first step and the properties of the obtained slurry, Table 6 shows the characteristics of the powder in the second step and the manufacturing conditions of the third step, and Tables 7 and 8 show the phosphoric acid obtained. The battery characteristics of the manganese iron lithium particle powder are shown in Table 9 and evaluated by a coin cell using the obtained lithium manganese iron phosphate particle powder as a positive electrode.

In the lithium iron manganese phosphate particles having an olivine structure according to the present invention, when the lithium and phosphorus contents satisfy Li ≧ P, the formation of an Mn ₂ P ₂ O ₇ impurity crystal phase that deteriorates battery characteristics Tended to be suppressed.

In addition, when the unit cell volume V _UC ( ^{３ 3} ) is in the relationship shown in the formula (1), the discharge capacity was higher and the battery performance tended to be good. This is presumably because the smaller the unit cell volume, the more lithium iron manganese phosphate having an olivine-type structure with less transition metal substitution to the Li site and fewer P and O defects.

In addition, in the lithium iron manganese phosphate particles having the olivine structure according to the present invention, the impurity crystal phase is not detected, but when Li and P are present out of the stoichiometric ratio, the excess Li It is believed that P and P do not adversely affect battery characteristics by forming an ion conductive amorphous phase.

Further, when the battery characteristics are evaluated with a coin cell by converting the lithium iron manganese phosphate particles according to the present invention into a positive electrode, a coin cell using an electrode in which the amount of the conductive material is doubled with respect to the evaluation method is 5C. The discharge capacity was improved by 10 to 30%, and a further increase in capacity was confirmed.

From the above results, the method for producing olivine-type lithium iron manganese phosphate particles according to the present invention can be achieved by using an approximately equal amount of raw material without using an excessive amount of raw material, and a low-cost and efficient production method. is there. In addition, the olivine-type lithium manganese iron particle powder having the olivine structure according to the present invention makes it possible to produce a positive electrode sheet having a high filling property, and a secondary battery using the same has a high capacity in terms of current load characteristics. It was confirmed that it was obtained.

The present invention uses olivine-type lithium iron manganese phosphate particles produced by a low-cost and efficient production method as a positive electrode active material, so that the energy density per volume is high and the capacity is high even in high current load characteristics. A non-aqueous electrolyte secondary battery can be obtained.

Claims (9)

1. Lithium iron manganese phosphate LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) particle powder manufacturing method of olivine type structure, with Li compound, Mn compound, Fe compound, P compound as raw material And sugar or organic acid, the raw material charge ratio is 0.95 ≦ Li / (Mn + Fe) ≦ 2.0, 0.95 ≦ P / (Mn + Fe) ≦ 1.3 in terms of mol ratio, and (Mn + Fe) A first step of obtaining an aqueous slurry having a pH of 5.5 to 12.5 by a neutralization reaction of a mixed solution containing 1 to 20 mol% of sugar or organic acid, the slurry obtained in the first step is reacted at a reaction temperature of 120 to Hydrothermal treatment is performed at 220 ° C., and the resulting compound has a production rate of LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) of 75 wt% or more, and the crystallite size is 10 to 250 nm. After the compound In the second step, the organic compound is added to the compound obtained in the second step in an amount of 3 to 40 wt% to obtain a precursor powder, and the precursor powder obtained in the third step has an oxygen concentration of 0.1. A method for producing olivine-type lithium iron manganese phosphate particles comprising a fourth step of baking at a temperature of 250 to 850 ° C. in an inert gas or reducing gas atmosphere of not more than 10%.
2. In the first step, the median diameter of the aggregated particles in the slurry is 0.1 to 10 μm, and the crystal phase is (NH ₄ ) Mn _1-α Fe _α PO ₄ (0 ≦ α <1) or HMn _1-β Fe _beta PO 4 the method according to claim 1 to obtain an aqueous slurry containing the aggregated particles is ₍₀ ≦ β <1).
3. The method according to claim 1 or 2, wherein the sugar or organic acid used in the first step is at least one of sucrose, ascorbic acid, and citric acid.
4. The production method according to any one of claims 1 to 3, wherein in the second step, washing is performed so that the sulfur content in the compound is 0.1 wt% or less.
5. The method according to any one of claims 1 to 4, wherein in the third step, the organic substance to be added is at least one of carbon black, an oil and fat compound, a sugar compound, and a synthetic resin.
6. Lithium manganese iron phosphate LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) particle powder having an olivine type structure, wherein the lithium and phosphorus content is 0.9 ≦ Li / mol (Mn + Fe) ≦ 1.2, 0.9 ≦ P / (Mn + Fe) ≦ 1.2, the BET specific surface area is 6 to 70 m ² / g, and the carbon content is 0.5 to 8 wt%. The sulfur content is 0.08 wt% or less, the amount of the crystalline phase LiMn _1-x Fe _x PO ₄ (0.05 ≦ x ≦ 0.5) of the olivine structure is 95 wt% or more, and the crystallite size is Phosphoric acid having an olivine structure characterized in that it has a median diameter of 25 to 300 nm, a median diameter of aggregated particles of 0.3 to 20 μm, and a powder electrical resistivity of 1 to 1.0 × 10 ⁶ Ω · cm Manganese iron lithium particle powder.
7. The olivine-type lithium manganese iron phosphate particle powder according to claim 6, wherein the lithium and phosphorus contents satisfy Li ≧ P.
8. The olivine type lithium manganese iron phosphate particle powder according to claim 6 or 7, wherein the unit cell volume V _UC is in the relationship of the formula (1).
   V _UC (Å ³ ) <11.4 × (1-x) +291.21 (1)
9. A non-aqueous electrolyte secondary battery produced using the olivine-type lithium iron manganese phosphate particles according to any one of claims 6 to 8.

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