WO2014034775A1 - Method for producing carbon composite lithium manganese iron phosphate particle powder, carbon composite lithium manganese iron phosphate particle powder, and nonaqueous electrolyte secondary battery using carbon composite lithium manganese iron phosphate particle powder - Google Patents

Abstract

The present invention provides a method for producing a carbon composite lithium manganese iron phosphate particle powder having an olivine structure (wherein the molar ratio Mn:Fe is from 0.98:0.02 to 0.50:0.50). This method for producing a carbon composite lithium manganese iron phosphate particle powder comprises: a first step wherein an aqueous suspension or water-containing material, which contains lithium manganese iron phosphate that has an olivine structure and is produced by a hydrothermal treatment, a lithium compound and/or a phosphorus compound, and an organic material, is obtained; a second step wherein a precursor mixture powder for firing is obtained by drying the aqueous suspension or water-containing material obtained in the first step; and a third step wherein the precursor mixture powder for firing obtained in the second step is fired. The present invention also provides: the carbon composite lithium manganese iron phosphate particle powder; and a secondary battery which uses the carbon composite lithium manganese iron phosphate particle powder. A carbon composite lithium manganese iron phosphate positive electrode active material having an olivine structure, which can be easily produced at low cost and exhibits excellent fillability, can be provided by this production method.

Description

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

As a positive electrode active material for a secondary battery that can be manufactured at low cost with low environmental impact, and has high output and high energy density, the present invention is a carbon composite that is excellent in low-temperature current load characteristics and excellent in high-temperature repeatability. Provided are lithium iron manganese phosphate 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, in addition to the 3.5 V class olivine type structure LiFePO ₄ , the same structure LiMnPO ₄ of 4.1 V class has attracted attention 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 , it is required to improve the charge / discharge characteristics and the repetition characteristics thereof.

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. In order to improve the electron conductivity and the electrode reaction, it is preferable to coat the particle surface of the positive electrode active material with carbon. 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 the following two-phase reaction is followed 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

According to a recent report, although a high capacity LiMnPO ₄ positive electrode was obtained by sufficiently combining positive electrode active material particles and carbon in terms of performance related to the entry and exit of Li, long-term stability of MnPO ₄ from which Li was desorbed There are various theories about. For this reason, it is considered necessary to prevent refinement due to particle cracking when Li is desorbed by a charging reaction, and to stabilize the crystal structure of the substance from which Li is desorbed. For example, there are techniques such as solid solution of Fe in Mn sites and fine particles of active material (Non-Patent Documents 1 to 7).

In LiMn _1-x Fe _x PO _{4 having} an olivine structure, the charge / discharge characteristics at low current are better as the particle surface is covered with carbon. Moreover, the charge / discharge characteristics under a high current load tended to be better as the fine particles having a crystallite size of less than 100 nm were satisfied. Moreover, in order to obtain a high molded body density as an electrode, each aggregate is formed so that they form a network with appropriately aggregated secondary particles and a conductive auxiliary agent such as carbon having a high graphitization rate. The state needs to be controlled. However, 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 ensure the charge / discharge capacity per unit volume, LiMn _1-x Fe _x PO ₄ that is fine and moderately coated with carbon is obtained, and a high density is obtained through a small amount of conductive auxiliary agent. There is a need to form aggregates.

A mechanochemical method in which LiMnPO ₄ particles and carbon are mechanically mixed is generally known as a means for compounding LiMnPO ₄ particles and carbon to increase the capacity. There are very few devices and conditions for mass production effectively. In addition, it is suggested that LiMn _1-x Fe _x PO ₄ has a catalytic effect of Fe, and carbon is deposited on the particle surface by a reaction in an inert gas of an organic substance, thereby improving its electric resistance. The degree of carbon coating is insufficient compared to LiFePO ₄ , and further surface modification of the particles is required (Non-Patent Documents 1 to 7).

As one method for modifying the particle surface of LiMn _1-x Fe _x PO ₄ , an amorphous phase composed of Li and P that easily moves Li and electrons, or an oxide composed of Li and P containing different elements is used on the surface. It has been proposed to form. However, it is difficult to say that industrial methods are mentioned.

Conventionally, in order to improve various characteristics of LiMn _1-x Fe _x PO ₄ particles, various improvements have been made by a solid phase reaction method, a hydrothermal reaction method, and a sol-gel method. For example, a technique for obtaining a high capacity by compounding with carbon having a high specific surface area (Patent Document 1), a technique for adding different metal elements to reduce electric resistance (Patent Document 2), adding a different metal element and carbon coating A technique for reducing electric resistance (Patent Document 3), a technique for synthesizing by a hydrothermal method, a sol-gel method (Patent Documents 4 to 6), and the like are known.

Special table 2011-517053 gazette JP 2004-063270 A Special table 2008-130525 gazette JP 2010-251302 A JP 2010-267501 A JP 2011-213587 A

A carbon composite LiMn _1-x Fe _x PO ₄ (0.02 ≦ x ≦ 0. 0) having a low electrical resistance, a high filling property, and an excellent charge / discharge repetition characteristic as a positive electrode active material for a non-aqueous electrolyte secondary battery. 5) The most demanding method for producing particle powder at low cost and low environmental load is currently in demand, but has not yet been established.

That is, in the techniques described in Non-Patent Documents 1 to 7, LiMn _1-x Fe _x PO ₄ (0.02 ≦ x ≦ 0) having low electric resistance, high filling property, and excellent charge / discharge repetition characteristics. .5) Particle powder cannot be obtained industrially.

The technique described in Patent Document 1 is a technique for improving the capacity when LiMn _1-x Fe _x PO ₄ particle powder is used as a positive electrode, and it touches on the filling property to the electrode and the control of the secondary aggregate state. Absent.

The technique described in Patent Document 2 is not a technique for obtaining high electronic conductivity by combining LiMnPO ₄ particle powder and carbon, and it is difficult to say that a high-capacity positive electrode active material can be obtained.

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 method using a water-soluble organic solvent having a high boiling point according to the hydrothermal method described in Patent Document 4 and an acetate salt according to the sol-gel method described in Patent Document 5 is hardly low-cost.

In addition, the main component adjustment method of Li, Mn, Fe, and P described in Patent Document 6 requires fine pulverization and high dispersion to nano-size with an apparatus such as a ball mill in order to mix adjustment additives in a dry manner. From the viewpoint of mass productivity, it was difficult to say that it was industrial.

Therefore, the present invention improves the crystallinity and surface properties of the positive electrode active material obtained after firing by optimizing the adjustment method of the main component composition ratio before firing, and has low electrical resistance and high fillability. Establishing an industrial manufacturing method of LiMn _1-x Fe _x PO ₄ (0.02 ≦ x ≦ 0.5) with a low environmental load, high output and high energy density, low temperature current load characteristics Another object of the present invention is to provide a carbon composite lithium manganese iron phosphate particle powder that is excellent in repetitive characteristics of charge and discharge at a high temperature and a secondary battery using the same.

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

That is, the present invention provides a method for producing olivine type carbon composite lithium manganese iron phosphate (Mn: Fe = 0.98: 0.02 to 0.50: 0.50 mol ratio) particle powder by hydrothermal treatment. The first step of obtaining an aqueous suspension or a hydrate containing the produced olivine-type lithium manganese iron phosphate and lithium compound and / or phosphorus compound and an organic substance, the aqueous suspension obtained in the first step Or the 2nd process which obtains the precursor mixed powder for baking by drying a hydrate, The carbon composite lithium manganese phosphate particle powder which consists of the 3rd process of baking the precursor mixed powder obtained by the 2nd process The aqueous suspension or water-containing product in the first step is 0.98 ≦ Li / (Mn + Fe) ≦ 1.20, 0.98 ≦ P / (Mn + Fe) ≦ 1.20 in terms of mol ratio. P ≦ Li is satisfied And a 60 wt% or _{Li 1-y H 2 + y} PO 4 of the lithium compound and / or phosphorus compounds (0 ≦ y ≦ 1), 1 ~ the organic substance in a phosphoric acid lithium manganese iron after the hydrothermal treatment It is a manufacturing method of the carbon composite lithium manganese iron phosphate particle powder which is 20 wt% (Invention 1).

In addition, the present invention provides a carbon composite lithium manganese iron phosphate particle powder in which the organic substance is a water-soluble organic substance in the first step of the method for producing the carbon composite lithium iron manganese phosphate particle powder described in the present invention 1. This is a manufacturing method (Invention 2).

In the first step of the method for producing carbon composite lithium iron manganese phosphate particles, the present invention provides a polyhydric alcohol, a sugar, or an organic substance in which the organic substance contains a hydroxy group (—OH) or a carboxyl group (—COOH). It is a manufacturing method of this invention 1 or 2 which is the organic substance which belongs to an acid (this invention 3).

Further, the present invention is the production method according to any one of the present inventions 1 to 3, wherein the drying temperature in the second step of the method for producing the carbon composite lithium manganese iron phosphate particle powder is 40 ° C. to 250 ° C. ( Invention 4).

Further, the present invention is a carbon composite lithium manganese iron phosphate particle powder obtained by the production method described in any of the present inventions 1 to 4 (Invention 5).

Further, the present invention is a non-aqueous electrolyte secondary battery produced using the carbon composite lithium manganese iron phosphate particle powder described in the present invention 5 (Invention 6).

The method for producing carbon composite lithium manganese phosphate particles according to the present invention is low in cost and can be produced with a small environmental load, and the powder obtained by the method has low electrical resistance and high filling properties. In addition, a secondary battery using it as a positive electrode active material has a high capacity in current load characteristics at low temperatures, and sufficiently withstands repeated charge and discharge even at high temperatures. Therefore, the carbon composite lithium manganese iron phosphate particles according to the present invention are suitable as a positive electrode active material for a non-aqueous electrolyte secondary battery.

2 is a high-magnification secondary electron image of the carbon composite lithium iron manganese phosphate particles obtained in Example 1 with a scanning electron microscope. 2 is a low-magnification secondary electron image of the carbon composite lithium iron manganese phosphate particles obtained in Example 1 with a scanning electron microscope. The carbon composite lithium manganese iron phosphate particle powder obtained in Example 1 is made positive, and the discharge capacity evaluated at 25 ° C. and 0 ° C. using a coin cell is dependent on the current load. It is the electric current load dependence of the discharge curve which made the carbon composite lithium manganese iron phosphate particle powder obtained in Example 1 positive electrode and evaluated at 0 ° C. using a coin cell. Charging / discharging curve (n = n) when the carbon composite lithium manganese iron phosphate particle powder obtained in Example 1 was made positive and cycle characteristics were evaluated using a coin cell between 60 ° C. and 2.0-4.5V. 1, 2, 12,... 10 × i, i = 1 to 6) and the discharge capacity in each cycle. Charging / discharging curve (n = n) when the carbon composite lithium manganese iron phosphate particle powder obtained in Example 1 was made positive and cycle characteristics were evaluated using a coin cell at 60 ° C. and between 2.0 and 4.3 V. 1, 2, 12,... 10 × i, i = 1 to 6) and the discharge capacity in each cycle.

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

First, a method for producing a carbon composite lithium manganese phosphate particle powder according to the present invention will be described.

The carbon composite lithium iron manganese phosphate particles according to the present invention are produced based on lithium iron manganese phosphate obtained by hydrothermal treatment.

Hydrothermal treatment is a method of synthesizing a compound under high temperature and high pressure by mixing aqueous solutions of raw material compounds. In the present invention, the method for obtaining lithium iron manganese phosphate by hydrothermal treatment is not limited, but the following method is preferably used in order to obtain fine lithium iron manganese phosphate with a high production rate.

The product obtained by the hydrothermal treatment is a fine Li _1-α Mn _1-x Fe _x P _1-β O _4-δ (0.02 ≦ x ≦ 0.5, 0 ≦ α) with a crystallite size of 200 nm or less. , Β ≦ 0.2). Here, α, β, and γ are crystallographic parameters, and α and β did not exceed 0.2. Further, δ is a parameter added to satisfy the electrical neutral condition.

As a raw material of carbon composite lithium manganese iron phosphate according to the present invention, Li source, LiOH.H ₂ O, Li ₂ CO ₃ , Mn raw material, MnSO ₄ .H ₂ O, MnCO ₃ , Fe raw material, FeSO ₄ .nH ₂ O, FeCO ₃ , P raw materials include H ₃ PO ₄ , (NH ₄ ) H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ , (NH ₄ ) ₃ PO _{4 and the} like. In addition, as raw materials obtained by combining main raw materials, there are Li ₃ PO ₄ , M ₃ (PO ₄ ) ₂ .nH ₂ O, (NH ₄ ) MPO ₄ .nH ₂ O (above, M = Mn, Fe) and the like. .

In the hydrothermal treatment, it is preferable to make the raw material fine particles so that the raw material mixing and dissolution / precipitation reaction can be performed quickly under the condition that many crystal nuclei of lithium iron manganese phosphate are generated. In order to make the raw material particles fine in the slurry, it is possible to perform pulverization using a medium such as a ZrO ₂ ball or to mix the raw materials at a high concentration. Examples of the apparatus used for pulverization include a ball mill and a medium stirring mill, and examples of the high concentration raw material mixing apparatus include a roller and a kneader.

Further, as an antioxidant for Fe during hydrothermal treatment, an organic acid such as ascorbic acid or citric acid or a reducing sugar such as glucose may be used. The amount is preferably 1 to 20 mol% with respect to (Mn + Fe), and Li _1−α Mn _1−x Fe _x P _1−β O _4−δ (0.02 ≦ x ≦ 0.5) after hydrothermal treatment. , 0 ≦ α, β ≦ 0.2), and the primary particle size of the product tends to be refined.

On the other hand, LiOH, NH ₃ , NaOH, Na ₂ CO ₃ , NH ₃ , urea, ethanolamine, or the like can be used as an alkali source during hydrothermal treatment. In order to increase the reaction rate of lithium manganese iron phosphate after hydrothermal treatment, the pH needs to be 5.5 to 12.5.

As the temperature and time of hydrothermal treatment are required, the reaction rate and particle size of lithium iron manganese phosphate tend to increase, but it is preferable to react at 90 to 300 ° C. for 2 to 3 hours.

In the X-ray diffraction measurement of the product after hydrothermal treatment obtained by this method, a crystal phase having an olivine structure is observed at 75 wt% or more. The product after hydrothermal treatment obtained by this method is lithium manganese iron phosphate containing almost no heterogeneous phase.

The reaction rate of lithium iron manganese phosphate after the hydrothermal treatment obtained by this method exceeds 80 wt%. The reaction rate of lithium manganese iron phosphate after the hydrothermal treatment was calculated from the ratio of weight loss before and after the heat treatment of the obtained particle powder at 700 ° C. for 2 hours in an inert gas atmosphere. For example, when a weight loss of 3 wt% occurs, the reaction rate is set to 100-3 = 97 wt%. Since the product after hydrothermal treatment obtained by this method is almost single-phase, it is thought that the weight loss is caused by water, carbon dioxide and the like.

After the hydrothermal treatment, in some cases, the product may be subjected to filtration washing or decantation washing for removal of impurity sulfate ions or ammonium ions and adjustment of the Li, Mn, Fe, and P composition ratios. Examples of the apparatus include a press filter and a filter thickener.

The first step of the present invention is to obtain an aqueous suspension or hydrate containing an olivine-type lithium iron manganese phosphate, a lithium compound and / or a phosphorus compound, and an organic substance produced by hydrothermal treatment. An aqueous slurry of lithium manganese iron phosphate obtained by hydrothermal treatment as a method of obtaining an aqueous suspension or hydrate containing lithium manganese iron phosphate and lithium compound and / or phosphorus compound and organic matter produced by hydrothermal treatment A method of adding a lithium compound and / or a phosphorus compound and an organic substance, and adding and mixing a lithium compound and / or a phosphorus compound and an organic substance to a cake obtained by dehydrating an aqueous slurry of lithium manganese iron phosphate obtained by hydrothermal treatment, Method of making water content, Method of adding lithium compound and / or phosphorus compound, organic substance and water to powder obtained by drying and finely pulverizing aqueous slurry of lithium iron manganese phosphate obtained by hydrothermal treatment to make water content Etc.

Lithium manganese iron phosphate produced by hydrothermal treatment has many defects in the crystal. Therefore, in order to form a desired lithium manganese iron phosphate solid solution with few defects, it is necessary to adjust the main component composition ratio before firing. That is, the main component composition ratio is 0.98 ≦ Li / (Mn + Fe) ≦ 1.15, 0.98 ≦ P / (Mn + Fe) ≦ 1 with respect to lithium iron manganese phosphate obtained by hydrothermal treatment. .15, P ≦ Li needs to be adjusted by adding a lithium compound and / or a phosphorus compound. Except for a predetermined composition ratio, an impurity phase is excessively generated, which causes deterioration of battery characteristics. That is, if Li / (Mn + Fe) is too small, α-Fe, (Mn + Fe) ₂ P, (Mn + Fe) ₃ P, (Mn + Fe) ₂ P ₂ O _7, etc. are excessively generated, and if too large, excessive Li ₂ CO ₃ remains. On the other hand, if P / (Mn + Fe) is too small, excess α-Fe, (Mn + Fe) ₂ O _{3 and the} like are generated, and if P / (Mn + Fe) is too large, Li ₃ PO ₄ and Li ₄ P ₂ O _{7 and the} like are excessively generated.

As the lithium compound used for adjusting the main component composition ratio in the present invention, LiOH, Li ₂ CO ₃ or the like can be used.

As the phosphorus compound used for adjusting the main component composition ratio in the present invention, H ₃ PO ₄ , (NH ₄ ) H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ , (NH ₄ ) ₃ PO _4, or the like is used. Can do.

Also used for adjusting the main component composition ratio, as a compound containing lithium and _phosphorus, it can be used _{LiH 2 PO 4, Li 3 PO} 4, LiPO 3 , and the like.

And in the main component composition ratio adjustment in the present invention, a lithium compound, a phosphorus compound, a compound containing lithium and phosphorus may be used in combination.

In the present invention, 60 wt% or more of the lithium compound and / or phosphorus compound added to adjust the composition ratio is Li _1-y H _{2 + y} PO ₄ (0 ≦ y ≦ 1). By using a large amount of Li _1-y H _{2 + y} PO ₄ as a lithium compound and / or phosphorus compound for adjusting the main component composition ratio, the carbon composite lithium manganese phosphate obtained after firing has a lattice of sites unique to each element. Defects are almost reduced, and a high-performance positive electrode active material can be obtained by increasing crystallinity. Preferably, 75 wt% or more is used with respect to the lithium compound and / or the phosphorus compound to which Li _1-y H _{2 + y} PO ₄ is added. As Li _1-y H _{2 + y} PO ₄ added to adjust the composition ratio, LiH ₂ PO ₄ is preferably used at 60 wt% or more, more preferably 75 wt% or more. When the amount of LiH ₂ PO ₄ used is less than 60 wt%, the adjustment of the main component composition ratio is not uniform at the individual particle level, and coarse Li ₃ PO ₄ and Li ₄ P ₂ O ₄ are produced excessively, It becomes a factor which deteriorates battery characteristics.

Li ₃ PO ₄ is preferably used because it easily forms water-insoluble fine particles of 50 nm or less and can be easily and uniformly mixed with lithium iron manganese phosphate before firing.

In the present invention, the aqueous suspension or hydrated product obtained in the first step needs to contain 1 to 20 wt% of organic matter relative to lithium iron manganese phosphate obtained by hydrothermal treatment. The amount of the organic substance is preferably 5 to 15 wt%. When the amount of the organic substance added is too small, the amount of residual carbon after firing is small, and the composite of lithium iron manganese phosphate and carbon by firing is insufficient. Also, alpha-Fe impurity phase when the addition amount of the organic material is too _{large, (Mn + Fe) 2 P} , (Mn + Fe) 3 P product is promoted, and is a cause of deteriorating the battery characteristics. As the organic substance to be added, a water-soluble or water-dispersible organic substance can be used, and it is particularly preferable to use a water-soluble organic substance for uniform improvement of the lithium manganese iron phosphate particle surface. Both water-soluble organic substances and water-dispersible organic substances may be used.

The water-soluble organic substance is preferably a water-soluble organic substance belonging to a polyhydric alcohol, sugar, or organic acid containing a hydroxy group (—OH) or a carboxyl group (—COOH), specifically, polyvinyl alcohol (PVA). Sucrose, citric acid, ethylene glycol and the like.

Examples of water-dispersible organic substances include hydrophilized synthetic fibers and carbon black, such as polyethylene particles, acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) and ketjen black (manufactured by Lion Co., Ltd.). On the other hand, it is necessary to modify the surface with an alkaline solution such as PVA having a hydrophilic group and a hydrophobic group, a nonionic surfactant (for example, polyoxyethylene ether), or LiOH.

In the present invention, lithium iron phosphate with an olivine structure produced by hydrothermal treatment and a lithium compound for adjusting the main component composition ratio and / or a phosphorus compound and an organic substance are mixed in the presence of water. Uniform mixing is achieved. As a result, the particle surface of lithium iron manganese phosphate is improved, and an olivine-type lithium iron manganese phosphate particle powder having high battery characteristics can be obtained by an industrial manufacturing method with a low environmental load. is there.

In particular, in the first step of the present invention, the lithium compound and / or phosphorus compound for adjusting the main component composition ratio is Li _1-y H _{2 + y} PO ₄ (0 ≦ y ≦ 1), and water is added as an organic substance to be added. When soluble organic matter is used, in order to cause a phosphate ester reaction and a polymerization reaction by dehydration by heating when drying and obtaining a precursor powder for firing in the second step, together with carbon obtained by firing, It is believed that the Li-P amorphous phase improves the surface of lithium manganese iron phosphate particles.

In the second step, the present invention dries the aqueous suspension or hydrate of lithium manganese iron phosphate obtained in the first step to obtain a precursor mixed powder for firing. The drying temperature is preferably 40 to 250 ° C. As a method for drying an aqueous suspension or a hydrated product, an aqueous slurry is mixed with a disper or the like and dried with a normal dryer, a method with a spray dryer or a slurry dryer, an aqueous cake or a dry powder with water. Examples include a method of kneading the hydrated product added with a roller and a kneader and drying with a normal dryer. In the present invention, Li _1-y H _{2 + y} PO ₄ used for adjusting the main component composition ratio is acidic, so that drying in a short time is desirable so as not to damage lithium iron manganese phosphate particles after hydrothermal treatment. (E.g., within 1 hour for a 500 g slurry).

In the aggregate particle size of the carbon composite lithium manganese iron phosphate particles according to the present invention, there is almost no change in the aggregate particle size before and after firing. Therefore, it is necessary to adjust the aggregate particle diameter between the first step and the second step or after the third step. The adjustment of the aggregate particle diameter can be controlled by the mixing / drying method, classification / pulverization in each step. Examples of the pulverizing apparatus include a high-speed impact pulverizer and an agate mortar.

In the third step of the present invention, the precursor powder mixture for firing obtained in the second 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. To do. As an apparatus for performing firing, there are a gas flow type box muffle furnace, a gas flow type rotary furnace, a fluidized heat treatment furnace, and the like. 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.

A trace amount of Fe ³⁺ contained in the Fe raw material is changed to Fe ²⁺ by an organic substance or a reducing gas to generate lithium iron manganese phosphate, and therefore a precursor for firing in an atmosphere having an oxygen concentration of 0.1% or less. It is necessary to fire the mixed powder. In order to complete the reaction of the unreacted substance and form a graphite phase having high electron conductivity from the added organic substance, it is preferable to perform heat treatment at 400 to 800 ° C. for several hours.

Next, the carbon composite lithium iron manganese phosphate particles according to the present invention will be described.

The carbon composite lithium manganese iron phosphate particles according to the present invention each have a lithium and phosphorus content of 0.98 to 1.15 in terms of a molar ratio to the transition metal, and the lithium content is not less than phosphorus. . When the contents of lithium and phosphorus are out of this range, high battery characteristics cannot be obtained because lithium manganese iron phosphate contains many different phases. Preferably, the lithium and phosphorus contents are 1.01 to 1.10, respectively, in molar ratio to the transition metal, and the lithium content is not less than phosphorus.

The unit cell volume of the carbon composite lithium iron manganese phosphate particles according to the present invention is determined by the unit cell volume V _UC of LiMn _1-x Fe _x PO ₄ having an olivine structure inferred from the Vegard law shown in the following formula 1. Since it is smaller than (Å ³ ), it is considered that there are almost no lattice defects in the crystal.
V _UC (Å ³ ) = 11.4 × (1-x) +291.21 (1)
Therefore, the ratio of the unit cell volume of the carbon composite lithium manganese iron phosphate particle powder according to the present invention to the unit cell volume V _{UC in} the formula (1) is preferably 99.950% or less.

The BET specific surface area of the carbon composite lithium iron manganese phosphate particles according to the present invention is preferably 6 to 70 m ² / g. When the BET specific surface area value is less than 6 m ² / g, the lithium iron manganese phosphate particles are large particles, and the movement of Li ions in the crystal is slow, so that it is difficult to extract current. When exceeding 70 m < ² > / g, since the fall with the packing density of a positive electrode and the reactivity with electrolyte solution increase, it is unpreferable. More preferably, it is 8 to 28 m ² / g, and even more preferably 9 to 20 m ² / g.

The carbon content of the carbon composite lithium manganese phosphate particles according to the present invention is preferably 0.7 to 8.0 wt%. When the carbon content is less than 0.7 wt%, the electric resistance of the obtained powder becomes high, and the charge / discharge characteristics of the secondary battery are deteriorated. On the other hand, when the content exceeds 8.0 wt%, the positive electrode filling density decreases, and the energy density per volume of the secondary battery decreases. More preferably, it is 1.0 to 4.0 wt%.

The carbon composite lithium manganese iron phosphate particle powder according to the present invention has an impurity sulfur content of 0.08 wt% or less, and good storage characteristics can be obtained in a non-aqueous electrolyte secondary battery. When the residual amount exceeds 0.08 wt%, impurities such as lithium sulfate are formed, and these impurities cause a decomposition reaction during charge and discharge, and the resistance increase during high temperature cycle characteristics becomes severe. More preferably, it is 0.05 wt% or less.

In the carbon composite lithium iron manganese phosphate particles according to the present invention, the crystal phase of Li ₃ PO ₄ may be detected at 5.0 wt% or less other than the olivine structure. Li ₃ PO ₄ itself does not actively contribute to charging and discharging, so 5.0 wt% or less is preferable. On the other hand, when Li ₃ PO ₄ is detected, the discharge capacity may be increased, more preferably 0. .1 to 3.0 wt%. It is desirable that the metal phase such as M ₂ P ₂ O ₇ (M = Mn, Fe) or Fe ₂ P as an impurity crystal phase should be minimized as a result of current load characteristics and high-temperature cycle characteristics.

The crystallite size of the carbon composite lithium manganese phosphate particles according to the present invention is preferably 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 as a result, the current load characteristic of the secondary battery is deteriorated. More preferably, it is 30 to 200 nm, and still more preferably 40 to 150 nm.

The agglomerated particle size of the carbon composite lithium manganese phosphate particles according to the present invention is preferably 0.3 to 30 μm. When the aggregated particle diameter is less than 0.3 μm, it is not preferable because the positive electrode packing density decreases and the reactivity with the electrolyte increases. On the other hand, when the aggregated particle diameter exceeds 30 μm, the electrode film thickness becomes closer, and there are cases where only a few particles are placed in the film thickness direction of the electrode, making sheeting extremely difficult. More preferably, it is 0.5 to 25 μm, and even more preferably 1.0 to 20 μm.

The compression-molded body density of the carbon composite lithium manganese phosphate particles according to the present invention is preferably 1.8 g / cc or more. The closer to the true density, the better the packing property, and the true density of the layered compound LiCoO ₂ often used as the positive electrode active material of the secondary battery is 5.1 g / cc, whereas the true density of lithium iron manganese phosphate is The density is as low as 3.5 g / cc. 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 molding density exceeding 2.8 g / cc while satisfying other powder characteristics by the production method of the present invention. It is considered that the carbon composite lithium manganese iron phosphate particles according to the present invention have a small amount of residual carbon, the primary particles are appropriately aggregated, and the density of the compression molded body is high.

The electric resistivity of the compression-molded body of carbon composite lithium iron manganese phosphate particles according to the present invention is preferably 1.0 × 10 ³ Ω · cm or less. If the electrical resistivity is low, the amount of the conductive material added when producing the positive electrode sheet can be reduced, and a positive electrode sheet having a high density can be obtained.

Next, a non-aqueous electrolyte secondary battery using carbon composite lithium iron manganese phosphate as a positive electrode active material in the present invention will be described.

When a positive electrode sheet is produced using the positive electrode active material according to the present invention, a conductive agent and a binder are added and mixed according to a conventional method. As the conductive agent, 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 75 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 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. Drying is performed at 80 to 180 ° C. to remove the solvent and soften the binder. 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. Therefore, it is desirable to carry out in a non-oxidizing atmosphere as much as possible.

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 0.1 to 10 ⁴ Ω · cm. Therefore, the amount of carbon added during sheet preparation can be reduced, 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 reduced, resulting in a high-density positive electrode. A 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.

The secondary battery manufactured using the positive electrode sheet of the present invention has a discharge capacity of 150 mAh / g or more at 0.1 C at 25 ° C., a discharge capacity at 1 C of room temperature of 140 mAh / g or more, and a discharge capacity of 5 C at room temperature. It is a characteristic of 120 mAh / g or more. Here, 0.1 C is a current value fixed so that a current of 170 mAh / g in theoretical capacity of LiMn _1-x Fe _x PO ₄ (0.02 ≦ x ≦ 0.5) flows in 20 hours. Is a current value fixed so that a current having a theoretical capacity of 170 mAh / g flows in 1 hour, and 5C is a current value fixed so that a current having a theoretical capacity of 170 mAh / g flows in 1/5 hour. A higher C coefficient means higher current load characteristics.

In addition, the secondary battery manufactured using the positive electrode sheet according to the present invention showed excellent characteristics in terms of current load characteristics at low temperatures and cycle characteristics at high temperatures, as shown in FIGS.

<Action>
The carbon composite lithium manganese iron phosphate particles according to the present invention are produced by hydrothermal treatment and heat treatment, and can be produced at low cost and with low environmental load. According to the production method of the present invention, the obtained carbon composite lithium iron manganese phosphate particle powder is controlled in crystallinity, particle surface, and aggregated particle size, and therefore when used as a positive electrode active material for a secondary battery. The present inventor presumes that a high capacity can be obtained even in current load characteristics at room temperature and low temperature, and that charging and discharging can be sufficiently repeated at high temperature.

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. The weight ratio of the additive was calculated by the amount charged.

The reaction rate of the hydrothermal treatment was evaluated by thermal analysis using an atmospheric tubular furnace (HS10S-2050TF, manufactured by Heat System Co., Ltd.). The dry powder of lithium iron manganese phosphate obtained by hydrothermal treatment was calculated from the ratio of weight loss before and after heat treatment at 700 ° C. for 2 hours in an inert gas atmosphere.

For the evaluation of the crystalline phase of lithium iron manganese phosphate in each step, the X-ray diffractometer SmartLab [manufactured by Rigaku Corporation] was used to measure under the conditions of Cu-Kα, 45 kV, 200 mA, and the Rietveld method was used. . The X-ray diffraction pattern was measured in steps of 0.02 ° with a counting time of 3.0 seconds and 2θ in the range of 15-90 ° so that the count number of the maximum peak intensity was 8000-15000. SRM674b of NIST (National Institute of Standards and Technology) was used as an external standard sample, and RIETA 2000 was used as a 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. The same method was used to evaluate the lattice constant (unit cell volume) and crystallite size of the electrode active material.

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

The Li, Mn, Fe, and P main elements of lithium manganese iron phosphate in each step were measured by ICP measurement using an emission plasma analyzer ICAP-6500 [manufactured by Thermo Fisher Scientific Co., Ltd.]. The sample was dissolved in an acid solution at 200 ° C. using an autoclave.

The powder evaluation of the carbon composite lithium manganese iron phosphate particles obtained by the present invention was performed as follows.

MONOSORB [manufactured by Yuasa Ionics Co., Ltd.] was used for the BET specific surface area after the sample was dried and deaerated under nitrogen gas at 120 ° C. for 45 minutes.

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

Agglomerated particle size using a Microtrac [Nikkiso Co., Ltd.] in the laser diffraction scattering type particle size distribution meter wet method and quantified in terms of median diameter D _50.

The density of the compression-molded body was compacted to 1.5 t / cm ² with a 13 mmφ jig and calculated from the weight and volume. At the same time, the electrical resistivity of the compression molded body was measured by the two-terminal method.

Hitachi S-4300 scanning electron microscope (SEM) was used for shape observation of the carbon composite lithium manganese phosphate obtained by the present invention.

Secondary battery characteristics by CR2032 type coin cell were evaluated using carbon composite lithium manganese iron phosphate particle powder.

The carbon of the conductive auxiliary agent used is acetylene black. The binder used was polyvinylidene fluoride (KF polymer manufactured by Kureha Co., Ltd.) having a polymerization degree of 630,000, and was dissolved in N-methylpyrrolidone (manufactured by Kanto Chemical Co., Inc.). As the electrode composition ratio A, the positive electrode material slurry was adjusted so that the electrode active material: acetylene black: PVDF = 88: 4: 8 by weight ratio, and applied onto the Al current collector with a doctor blade having a gap of 250 μm, After drying in air at 120 ° C. for 10 minutes, the dried sheet was pressurized to 3 t / cm ² to prepare a positive electrode sheet having a thickness of about 30 to 40 μm. Moreover, the positive electrode material slurry was adjusted so that the electrode composition ratio B was electrode active material: acetylene black: PVDF = 86: 7: 7 by weight ratio, and the same treatment was performed.

A positive electrode sheet punched to 2 cm ² , a 0.15 mm Li negative electrode punched to 17 mmφ, a separator (Celguard # 2400) in 19 mmφ, EC and DMC (ethylene carbonate: dimethyl carbonate = 3: 7) in which 1 mol / l LiPF ₆ was dissolved A CR2032-type coin cell (manufactured by Hosen Co., Ltd.) was prepared using an electrolytic solution (manufactured by Kishida Chemical Co., Ltd.) mixed in a volume ratio.

The discharge capacity at constant current values of 0.1 C, 1 C, and 5 C at 25 ° C. was evaluated in a coin cell using a positive electrode sheet having an electrode composition ratio A.

The current load characteristics at 0 ° C. and 25 ° C. were evaluated in a coin cell using a positive electrode sheet having an electrode composition ratio B. The current value during charging was a constant current value of 0.1 C, and discharging was performed at a constant current value corresponding to 0.1 to 5 C.

In addition, the charge / discharge curve / discharge capacity at 60 ° C. was evaluated in a coin cell using a positive electrode sheet having an electrode composition ratio B. Charge with a constant current value corresponding to 0.2 C, 1, 2, 12,..., 10 × i + 2 (i = 1 to 6) discharge at a constant current value corresponding to 0.2 C, others 1 C The discharge capacity of each cycle when discharged at a constant current value corresponding to is measured. The voltage range during charging and discharging was performed with a lower limit of 2.0 V, an upper limit of 4.5 V, a lower limit of 2.0 V, and an upper limit of 4.3 V.

[Example 1]
When the material balance of the transition metal was 100% in each step, the raw materials were weighed so that about 88 g (about 0.56 mol) of LiMn _0.8 Fe _0.2 PO ₄ was formed. MnSO _4, FeSO ₄ , H ₃ PO ₄ , NH ₄ OH, and pure water are mixed so that the transition metal becomes 5.6 mol / L, and NH ₄ MnPO ₄ and NH ₄ FePO ₄ are mixed by a neutralization reaction at room temperature. Got. After the precipitate was filtered off and washed with pure water, a solution of LiOH.H ₂ O, H ₃ PO ₄ , and ascorbic acid was added, and the molar ratio was Li: Mn: Fe: P = 1.05: 0. An aqueous slurry adjusted to a raw material charge ratio of 8: 0.2: 1.05 was obtained. The main crystal phase in the slurry was NH ₄ MnPO ₄ . The slurry was mixed with a ball mill, and the aggregated particles were pulverized to adjust the particle size.

The slurry was hydrothermally treated at 180 ° C. for 3 hours, and the obtained lithium iron manganese phosphate was washed with pure water using a Nutsche to obtain a cake. A part was extracted for evaluation and dried at 105 ° C. overnight. From the Rietveld analysis of the XRD diffraction pattern, the dry powder for evaluation was Li _1-α Mn _0.8 Fe _0.2 P _1-β O _4-δ (0 ≦ α, β ≦ 0.2) and 3.4 wt. % Impurity phase Li ₃ PO ₄ . Its composition ratio was Li: Mn: Fe: P = 1.00: 0.8: 0.2: 0.98 as measured by ICP, and 5.0 wt% weight loss was confirmed by thermal analysis. Was 95.0 wt%.

The cake obtained is peptized and a slurry is prepared. From the results of the reaction rate and the main component composition ratio, the lithium compound and / or phosphorus compound and organic matter are added and mixed so that the main component composition ratio shown in Table 1 is obtained. did. The main component composition ratio was confirmed by ICP measurement. Here, the addition amount of the organic substance in% by weight shown in Table 1 is a value with respect to the solid content obtained when the cake of lithium manganese iron phosphate obtained after the hydrothermal treatment is dried. (First step).

After adjusting the main component composition ratio, it was dried at 105 ° C. in the air. The dried product was pulverized with a coffee mill and sieved at 75 μm to obtain a precursor mixed powder with controlled aggregate particle size (second step).

The obtained precursor mixed powder for firing was placed in an alumina crucible and subjected to heat treatment at 700 ° C. for 5 hours in a nitrogen atmosphere. The temperature rising rate was 200 ° C./hr, and the N ₂ gas flow rate was 1 L / min. Then, it grind | pulverized with the agate mortar and sieved so that it might become 45 micrometers or less (3rd process).

The obtained powder was fine, and was carbon composite lithium manganese iron phosphate particle powder. Further, as a result of ICP measurement, the composition ratio of Li, Mn, Fe, and P adjusted in the first step was not different. 1 and 2 show high and low magnification SEM photographs (secondary electron images) of the carbon composite lithium manganese iron phosphate particles obtained. It was found that the obtained powder was composed of primary particles of 100 nm or less and agglomerated particles of several tens μm in which the primary particles were aggregated.

The powder characteristics of the obtained powder are shown in Table 2. Table 3 shows the battery characteristics obtained by making a positive electrode at the electrode composition ratio A and evaluated by the coin cell, and FIGS. 3 to 6 show the battery characteristics at the electrode composition ratio B. As shown in Table 3 and FIGS. 3 to 6, good results were obtained not only in the battery characteristics at 25 ° C. but also in the current load characteristics at 0 ° C. and the cycle characteristics at 60 ° C.

Table 1 shows the experimental conditions of the following examples and comparative examples, Table 2 shows the powder characteristics, and Table 3 shows the battery characteristics.

[Examples 2 and 3]
The lithium compound and / or phosphorus compound described in Table 1 and the carbon source were changed in the subsequent steps for the hydrothermal treatment and the lithium iron manganese phosphate particle-containing cake obtained after washing with the same specifications as in Example 1. In the same manner as in Example 1, drying, pulverization / classification, baking, and pulverization / classification were performed to obtain lithium iron manganese phosphate particles. Tables 2 and 3 show the evaluation results.

[Example 4]
After drying the cake containing lithium manganese iron phosphate particles after hydrothermal treatment and washing with the same specifications as in Example 1, using the lithium compound and / or phosphorus compound and carbon source listed in Table 1, 7 .5 wt% water was added and mixed in a coffee mill. Subsequent treatment was performed by the method described in Example 1 to obtain lithium iron manganese phosphate particles. Tables 2 and 3 show the evaluation results.

[Examples 5 and 6]
A cake was obtained by performing the same hydrothermal reaction precursor treatment, hydrothermal treatment, and water washing as in Example 1 except that the raw material charge ratio described in Example 1 was changed to Mn: Fe = 85: 15. . For evaluation, a part of the sample after washing with water was taken out and dried at 105 ° C. overnight, and Li _{1 -α} Mn _0.85 Fe _0.15 P _1-β O _4-δ was obtained by Rietveld analysis of the XRD diffraction pattern. It was found to contain (0 ≦ α, β ≦ 0.2) and 4.3 wt% of the impurity phase Li ₃ PO ₄ . The composition ratio was Li: Mn: Fe: P = 0.98: 0.85: 0.15: 0.96 by ICP measurement, and a 5.4 wt% weight reduction could be confirmed by thermal analysis. Was 94.6 wt%.

The lithium manganese phosphate particle-containing slurry obtained by peptizing the obtained cake was dried, pulverized and classified in the same manner as in Example 1 except that the lithium compound and / or phosphorus compound described in Table 1 and the carbon source were changed. Firing, pulverization and classification were performed to obtain lithium iron manganese phosphate particles. Tables 2 and 3 show the evaluation results.

[Comparative Example 1]
A cake was obtained by performing the same hydrothermal reaction precursor treatment, hydrothermal treatment, and water washing as in Example 1 except that the raw material charge ratio described in Example 1 was changed to Mn: Fe = 100: 0. . For evaluation, a part of the sample after washing with water was taken out and dried at 105 ° C. overnight. The result was 3.0 wt% impurity phase Li ₃ PO ₄ and Li _1-α MnP _{1-β in} the Rietveld analysis of the XRD diffraction pattern. It was found that O _4-δ (0 ≦ α, β ≦ 0.2). The composition ratio was Li: Mn: Fe: P = 0.98: 1.00: 0.0: 0.96 as measured by ICP, and a 4.8 wt% weight reduction could be confirmed by thermal analysis. Was 95.2 wt%.

The lithium manganese phosphate particle-containing slurry obtained by peptizing the obtained cake was dried, pulverized and classified in the same manner as in Example 1 except that the lithium compound and / or phosphorus compound described in Table 1 and the carbon source were changed. Firing, pulverization and classification were performed to obtain lithium iron manganese phosphate particles. Tables 2 and 3 show the evaluation results. In the coin cell using the electrode composition ratio B, a discharge capacity of 128 mAh / g (1C) was obtained at 0 ° C., and the capacity retention rate after 62 cycles at 60 ° C. was 98%.

Although the obtained powder was fine, the unit cell volume close to the formula (1) was obtained because LiMnPO ₄ itself hardly forms a defect structure. On the other hand, the battery characteristics are very poor and the carbon coating seems to be insufficient. At the same time, since the amount of carbon was large and the aggregated particle size was small, the density of the compression molded product was lowered.

[Comparative Example 2]
Example 4 except that the lithium compound and / or phosphorus compound and carbon source described in Table 1 were changed with respect to the cake containing lithium manganese iron phosphate particles after hydrothermal reaction and water washing obtained in the same specifications as in Example 1. Similarly, after drying the cake, the lithium compound and / or phosphorus compound, carbon source and water were mixed, re-dried, pulverized / classified, fired, and pulverized / classified to obtain lithium iron manganese phosphate particles. . Tables 2 and 3 show the evaluation results.

In Comparative Example 2, the amount of carbon source to be added was insufficient, and in Table 2, the amount of residual carbon was insufficient and the electric resistance was high. Therefore, the battery characteristics were also poor.

[Comparative Examples 3 and 4]
Example 1 except that the lithium compound and / or phosphorus compound and carbon source described in Table 1 were changed with respect to the cake containing lithium manganese iron phosphate particles after the hydrothermal reaction and water washing obtained in the same specifications as Example 1. In the same manner as above, after peptization of the cake, mixing, drying, pulverization / classification, firing, and pulverization / classification were performed to obtain lithium iron manganese phosphate particles. Tables 2 and 3 show the evaluation results.

Since Comparative Examples 3 and 4 did not use Li _1-y H _{2 + y} PO ₄ for adjusting the composition ratio, an undesirable impurity crystal phase was generated. As a result, it is surmised that the surface modification of the particles became insufficient and sufficient battery characteristics could not be obtained.

[Comparative Example 5]
The firing precursor mixed powder obtained in the second step in the same manner as in Example 1 is fired at 800 ° C., which is 100 ° C. higher than the other examples, pulverized and classified, and lithium manganese iron phosphate particles A powder was obtained. Tables 2 and 3 show the evaluation results.

The impurity phase Fe ₂ P was detected from the lithium iron manganese phosphate obtained in Comparative Example 5, and the unit cell volume was large, probably because Fe was reduced from the olivine structure. In addition, it was difficult to say that the battery characteristics shown in Table 3 were good because the impurity phase suppressed the modification of the particle surface.

When the current load characteristics at 0 ° C. were measured with the electrode composition B using the lithium iron manganese phosphate obtained in Comparative Example 5, it was far lower than the characteristics of Example 1 described in FIGS. Further, when a charge / discharge cycle test at 60 ° C. was performed between 2.0 and 4.5 V, the capacity suddenly decreased between 40 and 50 cycles and became almost 0 after 60 cycles. This is thought to be because the impurity phase Fe ₂ P was decomposed and deposited on the negative electrode side, causing internal short circuit and contamination of the Li negative electrode surface.

From the above results, the method for producing carbon composite lithium iron manganate particles according to the present invention is a low cost and low environmental load production method. In addition, the carbon composite lithium iron manganese phosphate particles according to the present invention can produce a highly filled positive electrode sheet, and a secondary battery using the positive electrode sheet has a current load at 25 ° C. and 0 ° C. It was confirmed that a high capacity was obtained in terms of characteristics. At the same time, as a result of the high-temperature charge / discharge cycle test at 60 ° C., a capacity retention rate of 98% or more was confirmed.

The present invention uses an olivine-type carbon composite lithium iron manganate particle powder produced by a low-cost, low environmental load manufacturing method as a secondary battery positive electrode active material, thereby increasing the energy density per volume. In addition, a high capacity can be obtained even in a low temperature, high current load characteristic, and a nonaqueous solvent secondary battery having a high capacity retention rate in a high temperature cycle characteristic can be obtained.

Claims (6)

1. Olivine-type structure produced by hydrothermal treatment in a method for producing olivine-type carbon composite lithium manganese iron phosphate (Mn: Fe = 0.98: 0.02-0.50: 0.50 mol ratio) particle powder First step of obtaining an aqueous suspension or hydrate containing lithium manganese iron phosphate, lithium compound and / or phosphorus compound and organic matter, drying the aqueous suspension or hydrate obtained in the first step A second step of obtaining a precursor mixed powder for firing, and a method of producing a carbon composite lithium manganese phosphate particle powder comprising a third step of firing the precursor mixed powder obtained in the second step. In the first step, the aqueous suspension or water-containing material satisfies 0.98 ≦ Li / (Mn + Fe) ≦ 1.20, 0.98 ≦ P / (Mn + Fe) ≦ 1.20, and P ≦ Li in molar ratios, And Richiu Above 60 wt% of the compound and / or phosphorus compound is _{Li 1-y H 2 + y} PO 4 (0 ≦ y ≦ 1), wherein the organic substance is 1 ~ 20 wt% with respect to manganese phosphate lithium iron after the hydrothermal treatment A process for producing carbon composite lithium iron manganese phosphate particles having an olivine structure.
2. The manufacturing method according to claim 1, wherein the organic substance is a water-soluble organic substance in the first step of the carbon composite lithium manganese iron phosphate particle powder manufacturing method.
3. In the first step of the method for producing carbon composite lithium manganese iron phosphate particles, the organic substance is a polyhydric alcohol containing a hydroxy group (—OH) or a carboxyl group (—COOH), a sugar, or an organic substance belonging to an organic acid. The manufacturing method of Claim 1 or 2.
4. The production method according to any one of claims 1 to 3, wherein the drying temperature in the second step of the production method of the carbon composite lithium iron phosphate particles is 40 ° C to 250 ° C.
5. Carbon composite lithium iron manganese phosphate particles obtained by the production method according to any one of claims 1 to 4.
6. A nonaqueous electrolyte secondary battery produced using the carbon composite lithium manganese phosphate particle powder according to claim 5.

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