JP5824723B2 - Method for producing positive electrode active material for lithium secondary battery, and lithium secondary battery using the same - Google Patents

Description

  The present invention relates to a method for producing a positive electrode active material for a lithium secondary battery, and a lithium secondary battery using the positive electrode active material for a lithium secondary battery.

  In recent years, small portable electronic devices such as digital cameras and mobile phones have been widely used. These electronic devices have always been required to minimize the volume and reduce the weight, and the batteries to be mounted are also required to be small, light, and have a large capacity. Also, in large-sized secondary batteries for automobiles and the like, it is desired to realize a large-sized nonaqueous electrolyte secondary battery instead of the conventional lead-acid battery.

  In order to meet such demands, lithium secondary batteries are being actively developed. As an electrode of a lithium secondary battery, a positive electrode in which an electrode mixture composed of a positive electrode active material containing lithium ions, a conductive additive, an organic binder, and the like is fixed to the surface of a current collector of a metal foil, and a lithium ion A negative electrode is used in which an electrode mixture composed of a removable negative electrode active material, a conductive additive, an organic binder, and the like is fixed to the surface of a current collector of a metal foil.

  Here, as a method for producing a positive electrode active material, a solid phase method, a coprecipitation method, a hydrothermal method and the like have been reported as in general inorganic synthesis, but from the viewpoint of cost, the number of steps is small, Solid phase methods that do not require solvents and excess amounts of raw materials are promising.

  As the metal element source, salts such as oxides, halides, inorganic acid salts, and organic acid salts are advantageous from the viewpoint of stability and cost. Among these, hydrates of these salts are often used as raw materials that are inexpensive, highly pure, and easily available. However, in the solid phase reaction, when a hydrate is used as a raw material, there is a problem that unreacted raw materials and reaction intermediates remain significantly and the purity of the product is lowered.

  For this problem, measures have been taken to use the hydrate raw material after dehydration by firing (Patent Document 1). However, the method of using the hydrate raw material after dehydration has a problem that a hydrate that does not form a stable anhydride cannot be used. In addition, since a large amount of energy and time is required for the firing process, it is disadvantageous from the viewpoint of manufacturing cost.

Further, as the positive electrode active material, lithium transition metal composite oxides such as lithium cobaltate, lithium manganate, and lithium nickelate are used. There are problems such as performance degradation due to composition change during discharge, and lithium oxyphosphorus complex oxides having an olivine structure have attracted attention as measures for improving these problems. Among them, lithium iron phosphate having an olivine structure represented by LiFePO ₄ is particularly practical because it contains abundant and inexpensive iron and has a potential of about 3.5 V with respect to metallic lithium. It is expected as a high material.

  However, lithium transition metal phosphorus composite oxides with an olivine structure are very poor in electronic conductivity compared to other positive electrode active materials and the like, and the conductivity of lithium ions in the crystal is also low, so primary particles are atomized. It is necessary to take measures such as (Patent Documents 2, 3, 4, 5) and covering with a conductive component (Patent Documents 6, 7, 8, 9, 10, 11). Furthermore, by using these methods in combination, the surface of finely divided primary particles is uniformly coated with conductive carbon generated by thermal decomposition of carbon-containing materials, so that the battery has a good discharge capacity close to the theoretical value. In addition, it has been reported that good charge / discharge characteristics at high load can be obtained (Patent Documents 1 and 12).

  Here, in Patent Document 12, high electron conductivity can be obtained by almost completely covering the surface of the positive electrode active material particles with carbon. However, since a carbon coating step is required separately from the firing step, there is a problem that the manufacturing cost increases.

In Patent Document 1, FePO ₄ , a lithium source, and a carbon-containing material are mixed and baked, so that the surface of the positive electrode active material is not subjected to a special carbon coating step, that is, with a relatively simple manufacturing method. Although it can be coated with carbon, in order to obtain a high discharge capacity, it is necessary to heat-treat the hydrate as a raw material in advance as described above, and the problem of an increase in manufacturing cost has not been solved.

JP 2009-295465 A Japanese Patent No. 4058680 Japanese Patent No. 4190912 JP 2002-015735 A JP 2008-159495 A Japanese Patent No. 4151210 Japanese Patent No. 4297406 JP 2004-063386 A JP 2007-250417 A JP 2008-034306 A Japanese Patent Laid-Open No. 2003-300734 JP 2006-302671 A

  The present invention has been made in view of such background art, and has a high discharge capacity and excellent charge / discharge characteristics at a low production cost without adding a special dehydration step to the hydrate as a raw material. An object of the present invention is to provide a method for producing a positive electrode active material for a lithium secondary battery.

That is, the present invention includes a lithium-containing compound, a transition metal salt sum thereof to obtain a mixture by mixing a reaction accelerator and (A), the step of firing the mixture at 300 ° C. or higher 900 ° C. or less (B) And the transition metal hydrate is FePO ₄ · 2H ₂ O, Fe ₃ (PO ₄ ) ₂ · 8H ₂ O or Mn (CH ₃ COO) ₂ · 4H ₂ O,
The reaction accelerator is a sulfate, nitrate or sulfide containing M ² or a hydrate thereof [wherein M ² is Fe (II), Co (II), Mn (II), Cu (II) , Mg (II), Fe (III) or NH ₄ (I). ]
It is related with the manufacturing method of the positive electrode active material material for lithium secondary batteries which is .

  Moreover, this invention relates to the manufacturing method of the said positive electrode active material material for lithium secondary batteries in which a reaction accelerator thermally decomposes at 900 degrees C or less.

The present invention, reaction accelerator, sulfates containing M ² or nitrates, or a hydrate thereof [where, M ² is Fe (II), Co (II ), Mn (II), Cu One or more selected from (II). ] It is related with the manufacturing method of the said positive electrode active material material for lithium secondary batteries.

The present invention also relates to a method for producing the positive electrode active material for a lithium secondary battery, wherein the transition metal salt hydrate is FePO ₄ .2H ₂ O.

  Moreover, this invention relates to the manufacturing method of the said positive electrode active material material for lithium secondary batteries which adds the carbon containing material which produces | generates conductive carbon further by thermal decomposition in a process (A).

  According to the present invention, a positive electrode active material for a lithium secondary battery having a high discharge capacity and excellent charge / discharge characteristics is produced at a low production cost without adding a special dehydration step to the hydrate as a raw material. A method can be provided.

FIG. 1 is an SEM image (50000 times) of Example 1. FIG. 2 is a TEM image (1200000 times) of Example 1.

  Hereinafter, the positive electrode active material for a lithium secondary battery in the present invention will be described.

  The positive electrode active material for a lithium secondary battery produced using the production method of the present invention is not particularly limited, but is a lithium transition metal composite oxide containing at least lithium and a transition metal, and a transition metal Is any one of Fe, Co, Ni, and Mn. In addition, you may contain 2 or more types of transition metals in one lithium transition metal complex oxide.

  Specifically, layered lithium nickel composite oxide, lithium cobalt composite oxide, lithium manganese composite oxide, lithium cobalt nickel composite oxide, lithium nickel manganese composite oxide, lithium cobalt nickel manganese composite Oxide,

  Spinel structure lithium manganese complex oxide,

  Examples thereof include lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate, lithium iron manganese phosphate and the like, which are lithium transition metal phosphorus-based composite oxides having an olivine structure.

  Among these, a lithium transition metal phosphorus-based composite oxide having an olivine structure is a preferable material from the viewpoints of cost and safety. Furthermore, with respect to lithium iron phosphate having an olivine structure, since the ratio of process cost to the manufacturing cost is large compared to other lithium transition metal composite oxides, the manufacturing cost can be greatly reduced by the manufacturing method of the present invention. Is also preferable.

  The lithium-containing compound used in the present invention is not particularly limited, but is preferably a lithium salt from the viewpoints of storage stability and ease of handling, and specifically, lithium oxide, lithium hydroxide, lithium chloride. , Lithium carbonate, lithium phosphate, and organic acid lithium such as lithium oxalate and lithium acetate. In particular, lithium carbonate is preferable because it is inexpensive and easily available. Two or more lithium-containing compounds can be used in combination.

As used in the present invention, a transition metal salt hydrate which is a hydrate containing M ¹ and containing no sulfur and nitrogen atoms in the compound [wherein M ¹ is Fe (II), Fe (III ) or Mn ( II ) . ] Is not particularly limited, as long as it is a hydrate containing M ¹ according to the target positive electrode active material for a lithium secondary battery and containing no sulfur atom and nitrogen atom in the compound. is a also available compounds, from the viewpoint of storage stability and easy handling, phosphates, or organic salts such as acetates, hydrates etc. are preferred.

M ¹ is preferably Fe (II), Fe (III ) or Mn (II ) from the viewpoint of abundant resources, and more preferably Fe (III) from the viewpoints of storage stability and ease of handling. preferable.

In the production of a positive electrode active material for lithium secondary battery which is transition metal phosphate lithium compound having an olivine structure, it is preferable to use hydrates of phosphates M ^1.

In general, transition metal salt hydrates are readily available, but can also be produced using a general method for synthesizing inorganic compounds. Specific examples include a coprecipitation method and a sol / gel method. For example, particle precipitation occurs by slowly mixing an ammonium dihydrogen phosphate aqueous solution and an iron (III) chloride aqueous solution, and the reaction solution is filtered, washed with water, and dried to produce amorphous FePO ₄ .nH _2. O can be obtained.

  Next, the reaction accelerator in the present invention will be described.

Reaction accelerator used in the present invention is a compound in a compound containing a sulfur atom and / or nitrogen atoms, specifically, sulfate, sulfide, and nitrate salts or the like. These hydrates can also be used.

In particular, sulfates, nitrates , sulfides, or hydrates thereof are preferably used. Further, a salt containing M ² [wherein M ² is Fe (II), Co (II), Mn (II) , Cu (II) , Mg (II), Fe (III) or NH ₄ (I) 1 type or 2 types or more selected. ] Is more preferable.

  The reaction accelerator is preferably thermally decomposed at 900 ° C. or lower.

The reaction accelerator is a sulfate or nitrate containing M ² or a hydrate thereof [wherein M ² is Fe (II), Co (II), Mn (II ), Cu (II) It is 1 type, or 2 or more types chosen from. It is more preferable that M ² is Fe (II), Co (II), or Mn (II).

From the viewpoint of the purity of the lithium secondary battery positive electrode active material obtained, it is preferably M ² is the same element as M ^1.

  The effect of the reaction accelerator in the present invention will be described below.

  In the reaction in the solid phase, different raw materials come into contact with each other, and the substance moves inside the particles by diffusion, so that a chemical reaction proceeds and a target compound is generated. However, in general, the diffusion rate of the substance inside the particles is extremely slow, and the purity of the product may be lowered due to unreacted raw materials and reaction intermediates remaining. For the purpose of completing the reaction, high temperature and / or prolonged heating may be carried out. However, when the raw material contains a volatile component such as an alkali metal compound or a carbon-containing compound, the composition ratio changes and Impurity generation can reduce the purity of the product.

  Furthermore, when using a hydrate as a raw material, since the water vapor | steam generated in a baking process inhibits reaction, the residue of an unreacted raw material and a reaction intermediate becomes remarkable, and the purity of a product may fall. Although the mechanism has not yet been elucidated, it is presumed that a hydroxyl group is generated on the surface of the raw material or product during firing to form a surface with poor reactivity. It is also conceivable that water molecules in the solid phase inhibit ion diffusion and ion pair formation.

  The reaction accelerator of the present invention has the effect of accelerating the solid phase reaction and improving the purity of the product by activating the surface of the raw material and reaction intermediate and the inside of the solid phase. For this reason, the purity of the obtained positive electrode active material for a secondary battery is improved, and a high discharge capacity can be obtained.

  According to the production method of the present invention, in the step of firing the raw material mixture, ions containing sulfur atoms and / or nitrogen atoms contained in the reaction accelerator are dissolved in the solid phase of the raw material and the reaction intermediate, In the solid phase of the raw material and the reaction intermediate, ion diffusion is facilitated by the formation of lattice vacancies and the generation of strain, and the reaction is considered to be promoted. In addition, as a solid solution mode, substitutional solid solution and interstitial solid solution can be considered.

  Further, when the reaction accelerator is decomposed in the firing step, a gas containing sulfur atoms and / or nitrogen atoms is generated. As the generated gas molecules are adsorbed and bonded to the raw material surface, disorder of atomic arrangement or ion vacancies are formed on the particle surface, and the reaction is promoted.

  Here, when the reaction accelerator is a compound containing a sulfur atom and / or a nitrogen atom in a compound that decomposes at a firing temperature or lower, in the firing step, the reaction accelerator is independent regardless of the reaction with other raw materials. Since pyrolysis occurs, gas can be generated reliably. For this reason, it is preferable that the reaction accelerator thermally decomposes at 900 ° C. or less.

  As a reaction accelerator which is a compound containing a sulfur atom and / or a nitrogen atom in a compound, sulfate, nitrate, sulfite, nitrite, nitride, or sulfide, or a hydrate thereof is available at a low price. It is preferable because it is easy. In particular, hydrates are more preferable because they are highly pure, inexpensive and easily available.

  In particular, when sulfate or nitrate is used as a reaction accelerator, the oxidizing gas molecules generated by the thermal decomposition of the reaction accelerator are compared with other raw materials on the surface of the raw material as compared with gases containing other sulfur atoms and / or nitrogen atoms. It is highly effective in promoting the reaction because it has a high effect of adsorbing and binding to and forming disorder of atomic arrangement or forming ion vacancies.

  Furthermore, when sulfate or nitrate is used as a reaction accelerator, in the step of firing the raw material mixture, sulfate ions and nitrate ions contained in the reaction accelerator are dissolved in the solid phase of the raw material and reaction intermediate. In the solid phase of the raw material and the reaction intermediate, it is considered that ion diffusion is facilitated by formation of lattice vacancies and generation of strain, and the effect of promoting the reaction is high. In addition, as a solid solution mode, substitutional solid solution and interstitial solid solution can be considered.

  In particular, when producing a positive electrode active material for a lithium secondary battery, which is a lithium transition metal lithium compound having an olivine structure, sulfate ions or nitrate ions are phosphorous in the solid phase of the raw material and reaction intermediate in the firing step. Acid sites can be replaced. For this reason, solid solution is easy to proceed, and a high reaction promoting effect is exhibited.

As a reaction accelerator, a compound containing M ² or a hydrate thereof [provided that M ² is one selected from Fe (II), Co (II), Mn (II) and Cu (II) or 2 or more types. ], Since the ionic radius of M ² is close to the ionic radius of the element contained in the raw material, it can be easily substituted and dissolved in the raw material and the reaction intermediate in the step of firing the raw material mixture. When M ² ions contained in the reaction accelerator are dissolved in the raw material, ion diffusion is facilitated by the generation of lattice vacancies and / or strains in the solid phase of the raw material and the reaction intermediate, and the reaction is promoted.

Furthermore, when the reaction accelerator is a very stable compound, it is difficult for the M ² contained in the reaction accelerator to be dissolved in the raw material from the viewpoint of the reaction rate. Pyrolysis is preferred.

Further, as a reaction accelerator, with a compound containing M ^2, it is possible to adjust the composition ratio of the mixture obtained by mixing raw materials. For example, a positive electrode active material for a lithium secondary battery, which is lithium iron phosphate having an olivine structure using iron (III) phosphate as a hydrate containing M ¹ and not containing a sulfur atom and / or a nitrogen atom In this case, the molar ratio Fe / P in the iron (III) phosphate to be used is less than the stoichiometric ratio of 1 (1-x) [where 0 <x <1]. At this time, a transition metal lithium phosphate having an olivine structure represented by the general formula LiFe _(1-x) M ² _x PO ₄ is produced by adding an appropriate amount (x) of a compound containing M ^2. Can do. In such a case, M ¹ and M ² are preferably made of the same element from the viewpoint of purity.

Sulfates, nitrates or their hydrates containing M ² have a thermal decomposition temperature of 800 ° C. or lower, and in the firing process, they are surely thermally decomposed independently of reaction with other raw materials. It is also a preferable reaction accelerator from the viewpoint that gas can be generated.

  As the addition amount of the reaction accelerator, the ratio of the sulfur atom and nitrogen atom content (mol) in the reaction accelerator to the lithium atom content (mol) in the lithium-containing compound is 0.1 mol% or more, It is 20 mol% or less. When this ratio is less than 0.1 mol%, the above effect cannot be obtained sufficiently. When it exceeds 20 mol%, the reaction accelerator and / or the compound derived from the reaction accelerator is a positive electrode active material for a lithium secondary battery. The weight ratio remaining inside becomes high, and the discharge capacity per unit weight in the material becomes low.

  The addition amount of the reaction accelerator is preferably 1 mol% or more and 10 mol% or less, and more preferably 2 mol% or more and 5 mol% or less.

Further, the reaction accelerator, sulfates containing M ^2, nitrates, or sulfide, or a hydrate thereof [where, M ² is Fe (II), Co (II ), Mn (II), Cu It is one or more selected from (II) , Mg (II), Fe (III) or NH ₄ (I) . ] Will be described below.

When producing a positive electrode active material for a lithium secondary battery that is a lithium transition metal composite oxide having a layered structure or a lithium transition metal phosphorus composite oxide having an olivine structure, a step of obtaining a mixture by mixing raw materials ( In A), the ratio of the sum of the content (mol) of M ¹ atom and the content (mol) of M ² atom to the content (mol) of lithium atom in the mixture is 0.90 or more and 1.10 or less It is. When this ratio is less than 0.90, or when it exceeds 1.10, there is a high possibility that impurities other than the lithium transition metal complex acid compound are contained, and in the positive electrode active material for the lithium secondary battery. Since the content of the lithium transition metal complex acid compound per unit weight in the battery is reduced, good battery performance may be difficult to obtain. This ratio is preferably 0.95 or more and 1.05 or less, and more preferably 0.97 or more and 1.03 or less.

In the production of a positive electrode active material for lithium secondary batteries is a lithium transition metal composite oxide having a spinel structure, in step (A), containing the M ¹ atom to the content of the lithium atoms in the mixture (mol) The ratio of the sum of the amount (mol) and the content (mol) of M ² atoms is 1.80 or more and 2.20 or less. When this ratio is less than 1.80 or more than 2.20, the possibility of containing impurities other than the lithium transition metal complex acid compound is high, and in the positive electrode active material for lithium secondary battery Since the content of the lithium transition metal complex acid compound per unit weight in the battery is reduced, good battery performance may be difficult to obtain. This ratio is preferably 1.90 or more and 2.10 or less, and more preferably 1.95 or more and 2.05 or less.

Moreover, when manufacturing the positive electrode active material material for lithium secondary batteries which is a phosphoric acid transition metal lithium compound which has an olivine structure using phosphate as a raw material, in step (A), the inclusion of phosphorus atoms in the mixture The ratio of the sum of the content (mol) of M ¹ atoms and the content (mol) of M ² atoms to the amount (mol) is 0.90 or more and 1.10 or less. When this ratio is less than 0.90 or exceeds 1.10, the possibility of containing impurities other than the lithium phosphate transition metal compound having an olivine structure is high, and the positive electrode for a lithium secondary battery Since the content of the lithium transition metal lithium compound having an olivine structure per unit weight in the active material is reduced, good battery performance may be difficult to obtain. This ratio is preferably 0.95 or more and 1.05 or less, and more preferably 0.97 or more and 1.03 or less.

  The carbon-containing material that generates conductive carbon by pyrolysis used in the present invention means that conductive carbon is generated by thermal decomposition, and the surface of the positive electrode active material particles is coated with the generated conductive carbon, thereby achieving high electronic conductivity. It is a material that can be obtained.

  Examples of carbon-containing materials include bitumens, saccharides, thermoplastic resins, aliphatic hydrocarbons, aliphatic alcohols, aliphatic carboxylic acids, alicyclic hydrocarbons, alicyclic alcohols, alicyclic carboxylic acids, natural Examples of the material include natural wax, natural resin, and vegetable oil, but the material is not particularly limited thereto.

  These materials can also be used in combination of two or more kinds of carbon-containing materials. Further, these carbon-containing materials can be used by being dissolved or dispersed in a medium such as a solvent or water.

  Examples of the bitumen include natural asphalt, petroleum asphalt obtained in the crude oil refining process, coal tar obtained in the coal refining process, and the like. Furthermore, pitches and resins obtained from these are also included.

  Examples of the saccharide include monosaccharides, disaccharides, oligosaccharides, and polysaccharides.

  Examples of the thermoplastic resin include polyolefins, acrylic resins, polyamides, polyesters, polycarbonates, polyethers, cellulose resins, and synthetic rubbers. Moreover, the modified body, mixture, or copolymer of these resin may be sufficient.

  Aliphatic hydrocarbons and alicyclic hydrocarbons are not particularly limited and can be used as long as they are liquid or solid at normal temperature and pressure, but from the viewpoint of carbon content and ease of handling, the number of carbons. Ten or more hydrocarbons are preferred. Also, a mixture of paraffin, liquid paraffin, petroleum wax and the like can be used.

  Aliphatic alcohols and alicyclic alcohols are not particularly limited and can be used as long as they are liquid or solid at normal temperature and normal pressure. From the viewpoint of carbon content and ease of handling, the number of carbons is 3 or more. Or a dihydric or higher alcohol.

  The aliphatic carboxylic acid and the alicyclic carboxylic acid are not particularly limited and can be used as long as they are liquid or solid at room temperature and normal pressure, but from the viewpoint of carbon content and ease of handling, the number of carbons. Five or more carboxylic acids are preferred.

  Examples of the natural material include natural wax, natural resin, vegetable oil, and the like, and these can be used after being modified. Examples of natural waxes include plant waxes and mineral waxes. Examples of the natural resin include non-volatile solid or semi-solid substances contained in the sap secreted from the bark, and resinous substances secreted by the scale insects parasitic on the tree.

  The optimum amount of carbon-containing material that generates conductive carbon by pyrolysis varies depending on the carbon-containing material, and is adjusted to the conductive carbon content in the positive electrode active material for lithium secondary batteries after thermal decomposition. It is desirable to weigh. The content of the conductive carbon is 0.1% by weight or more and 30% by weight or less, preferably 0.5% by weight or more and 20% by weight or less, more preferably 1% by weight or more and 15% by weight or less. When the conductive carbon content is less than 0.1 wt%, sufficient electron conductivity is not obtained, and when it exceeds 30 wt%, the weight of the generated conductive carbon in the positive electrode active material for the lithium secondary battery The ratio increases and the discharge capacity per unit weight in the material decreases.

The method for producing a positive electrode active material for a lithium secondary battery according to the present invention includes a lithium-containing compound and a transition metal salt hydrate which is a hydrate containing M ¹ and containing no sulfur atom and nitrogen atom in the compound [however, , M ¹ is Fe (II), Fe (III ) or Mn (II ) . And a reaction accelerator that is a compound containing a sulfur atom and / or a nitrogen atom in the compound to obtain a mixture (A), and a step of firing the mixture at 300 ° C. or more and 900 ° C. or less (B ) And is not limited to one method.

  The production method of the present invention may include a step of coating part or all of the surface of the positive electrode active material for secondary battery with a conductive component. Specifically, the method of coating with conductive particles, particles For example, a method of coating with conductive carbon that is not in the shape of a film. However, from the viewpoint of coating uniformity, a step of coating a part or all of the surface of the positive electrode active material for secondary battery with carbon by adding a carbon-containing material that generates conductive carbon by thermal decomposition. Is preferred. Furthermore, from the viewpoint of production cost, a method of adding a carbon-containing material that generates conductive carbon by thermal decomposition in the step (A) is more preferable.

  As one method for producing a positive electrode active material for a lithium secondary battery in the present invention, when synthesizing a lithium transition metal composite oxide, a lithium-containing compound, a transition metal salt hydrate, and conductive carbon by thermal decomposition are used. A method including a step of mixing a carbon-containing material that generates a reaction accelerator with a reaction accelerator, and a step of heating and reacting the mixture.

  In this production method, a lithium transition metal composite oxide formation reaction during heating and a conductive carbon formation reaction by pyrolysis of a carbon-containing material proceed simultaneously, and finally a lithium transition in which conductive carbon is treated on the surface. A metal composite oxide is obtained.

  Further, as one of the methods for producing a positive electrode active material for a lithium secondary battery in the present invention, when a lithium transition metal phosphorus composite oxide having an olivine structure is synthesized, a lithium-containing compound and a transition metal salt hydrate And a production method including a step of mixing a phosphorus-containing compound and a carbon-containing material that generates conductive carbon by thermal decomposition to form a mixture, and a step of heating and reacting the mixture.

  In this production method, the formation reaction of the lithium transition metal phosphorus-based composite oxide having an olivine structure during heating and the formation reaction of conductive carbon by thermal decomposition of the carbon-containing material proceed at the same time, and finally the conductive carbon becomes the surface. Thus, a lithium transition metal phosphorus-based composite oxide having an olivine structure treated in the above manner can be obtained.

  Regarding lithium transition metal phosphorus-based composite oxides having an olivine structure, conventionally, firing is performed separately from the step of synthesizing a lithium transition metal phosphorus-based composite oxide having an olivine structure as a carbon coating treatment step or a raw material dehydration treatment. Although there existed the subject that a process was needed, according to this manufacturing method, since a special process is not required, a manufacturing process can be simplified.

  In particular, for lithium iron phosphate having an olivine structure, compared to other lithium transition metal composite oxides, there was a problem that the ratio of the process cost compared to the raw material cost, the production method of the present invention, The manufacturing cost can be greatly reduced.

  Furthermore, as one of the methods for producing a positive electrode active material for a lithium secondary battery in the present invention, when a lithium transition metal composite oxide is synthesized, a lithium-containing compound, a transition metal salt hydrate, and a reaction accelerator are included. A step of mixing into a mixture; a step of heating and reacting the mixture; and a step of mixing with a carbon-containing material that generates conductive carbon by thermal decomposition to form a mixture; and a step of heating and reacting the mixture. The method containing is mentioned.

  Furthermore, as one of the methods for producing a positive electrode active material for a lithium secondary battery in the present invention, when a lithium transition metal phosphorus composite oxide having an olivine structure is synthesized, a lithium-containing compound and a transition metal salt hydrate And a step of mixing a phosphorus-containing compound and a reaction accelerator to form a mixture, and after heating and reacting the mixture, the mixture is mixed with a carbon-containing material that generates conductive carbon by thermal decomposition to form a mixture. The method of including a process and the process of heating and reacting the said mixture is mentioned.

  Furthermore, as one of the methods for producing a positive electrode active material for a lithium secondary battery in the present invention, when a lithium transition metal composite oxide is synthesized, a lithium-containing compound, a transition metal salt hydrate, and a reaction accelerator are included. Examples of the method include a step of mixing into a mixture and a step of heating and reacting the mixture and then coating with conductive particles by a dry or wet process.

  Here, the conductive particles are materials that can obtain high electron conductivity by being combined with a lithium transition metal composite oxide. Examples of the conductive particles include carbon particles, metal particles, metal oxide particles, etc. Among them, the most preferable material is carbon particles having high conductivity, little influence on battery performance, and low cost. It is a seed. Two or more kinds of conductive particles can be used in combination.

  The carbon particles are not particularly limited as long as they are conductive carbon materials, but it is possible to use carbon black, carbon nanotubes, carbon nanofibers, fullerenes, etc. alone or in combination of two or more. it can. From the viewpoint of conductivity, availability, and cost, it is preferable to use carbon black.

  Furthermore, as one of the methods for producing a positive electrode active material for a lithium secondary battery in the present invention, when a lithium transition metal phosphorus composite oxide having an olivine structure is synthesized, a lithium-containing compound, a transition metal salt hydrate, A step (A) in which a phosphorus-containing compound and a reaction accelerator are mixed to form a mixture, and a step (B) in which the mixture is heated and reacted and then coated with conductive particles by a dry or wet process. The method of including is mentioned.

  Specifically, the step (A) of mixing the transition metal salt hydrate, the lithium-containing compound, and the reaction accelerator, the step of mixing the carbon-containing material that generates conductive carbon by thermal decomposition, or coating the conductive particles Examples of the apparatus used in the process include the following dry processing machines and wet processing machines.

As a dry processing machine, for example,
Roll mills such as 2-roll and 3-roll, high-speed stirrers such as Henschel mixer and super mixer, fluid energy pulverizers such as micronizer and jet mill, attritor, particle compounding device “Nauta mixer” manufactured by Hosokawa Micron, “cyclomix” ”,“ Nanocure ”,“ Nobilta ”,“ Mechanofusion ”, powder surface modification device“ Hybridization system ”,“ Mechanomicros ”,“ Miraro ”, etc. manufactured by Nara Machinery Co., Ltd.

  In addition, when using a dry processing machine, other raw materials may be added directly to the raw material powder as a base material, but in order to produce a more uniform mixture, a small amount of other raw materials is used in advance. It is preferable to add it while dissolving or dispersing in the above solvent and dissolving the agglomerated particles of the raw material powder as the base material. Furthermore, it may be preferable to heat in order to increase the processing efficiency.

  Among the carbon-containing materials that generate conductive carbon by thermal decomposition, there are materials that are solid at room temperature, but have a low melting point and softening point of less than 100 ° C. When using such materials, they are mixed at room temperature. In some cases, it is possible to mix more uniformly by melting and mixing under heating.

As a wet processing machine, for example,
Mixers such as dispersers, homomixers, or planetary mixers;
Homogenizers such as “Clairemix” manufactured by M Technique or “Fillmix” manufactured by PRIMIX;
Media-type dispersers such as paint conditioners (manufactured by Red Devil), ball mills, sand mills (such as “Dynomill” manufactured by Shinmaru Enterprises), attritors, pearl mills (such as “DCP mill” manufactured by Eirich), or coball mills;
Wet jet mill (“Genus PY” manufactured by Genus, “Starburst” manufactured by Sugino Machine, “Nanomizer” manufactured by Nanomizer, etc.) “Claire SS-5” manufactured by M Technique, or “Micros manufactured by Nara Machinery Co., Ltd.” Medialess dispersers such as
Other examples include, but are not limited to, roll mills and kneaders. Moreover, it is preferable to use what performed the metal mixing prevention process from an apparatus as a wet processing machine.

  For example, when using a media-type disperser, a disperser in which the agitator and vessel are made of a ceramic or resin disperser, or the surface of the metal agitator and vessel is treated with tungsten carbide spraying or resin coating. Is preferably used. And as a medium, it is preferable to use ceramic beads, such as glass beads, zirconia beads, or alumina beads. Moreover, also when using a roll mill, it is preferable to use a ceramic roll. Only one type of dispersion device may be used, or a plurality of types of devices may be used in combination.

  Moreover, in order to improve the wettability and dispersibility of each raw material in a solvent, a general pigment dispersant can be added together and dispersed and mixed.

  In the method for producing a positive electrode active material for a lithium secondary battery in the present invention, the heating temperature in the firing step (B) varies depending on the raw materials, but is 300 to 900 ° C, preferably 450 to 800 ° C. Is desirable.

  When the heating temperature in a baking process (B) is less than 300 degreeC, the thermal decomposition of the carbon containing material which produces | generates conductive carbon by heat decomposition does not arise easily, and conductive carbon may be hard to produce | generate. On the other hand, when the heating temperature exceeds 900 ° C., the conductive carbon generated by the pyrolysis of the carbon-containing material is easily lost by combustion, and further battery performance other than the target lithium iron phosphate compound having an olivine structure is achieved. Impurities such as reduced iron oxide and iron phosphide are likely to be generated.

  Furthermore, the atmosphere in the firing step (B) varies depending on the target positive electrode active material for the lithium secondary battery, but it is an air atmosphere, an inert gas atmosphere such as nitrogen or argon, and a reduction containing hydrogen. A gas atmosphere.

  In particular, when using a carbon-containing material that generates conductive carbon by thermal decomposition, it is easy to burn and disappear easily with oxygen. Therefore, in order to efficiently generate conductive carbon, it is inert that contains as little oxygen as possible. It is preferable to carry out in a gas atmosphere or a reducing gas atmosphere.

  In addition, even when the positive electrode active material for the lithium secondary battery to be manufactured is a lithium transition metal phosphorus composite oxide having an olivine structure, the transition metal is easily oxidized by oxygen and the lithium transition metal phosphorus composite is different from the intended purpose. Since oxides may be generated, it is preferable to carry out in an inert gas atmosphere or a reducing gas atmosphere that does not contain oxygen as much as possible.

  Next, an electrode using the positive electrode active material for a lithium secondary battery in the present invention will be described.

  Regarding the electrode, an electrode mixture composed of at least a positive electrode active material for a lithium secondary battery and a binder in the present invention is coated on a current collector. Furthermore, in order to improve the electroconductivity of an electrode, a conductive support agent can also be added in an electrode mixture. Incidentally, it is preferable to use an aluminum foil for the positive electrode as the current collector.

  The composition ratio in the electrode mixture which comprises the electrode in this invention is as follows.

  The composition ratio of the positive electrode active material for a lithium secondary battery is desirably 70% by weight or more and 99.0% by weight or less, preferably 80% by weight or more and 95% by weight or less in the electrode mixture. When the composition ratio of the positive electrode active material for a lithium secondary battery is less than 70% by weight, it may be difficult to obtain sufficient conductivity and discharge capacity. When the composition ratio exceeds 98.5% by weight, the ratio of the binder is increased. Therefore, the adhesion to the current collector may be reduced, and the positive electrode active material for the lithium secondary battery may be easily detached.

  The composition ratio of the binder is desirably 1 to 10% by weight, preferably 2 to 8% by weight in the electrode mixture. When the composition ratio of the binder is less than 1% by weight, the binding property is lowered, so that the positive electrode active material for the lithium secondary battery and the conductive assistant may be easily detached from the current collector. When it exceeds, since the ratio of the positive electrode active material material for lithium secondary batteries will fall, it may lead to the fall of battery performance.

  The composition ratio of the conductive assistant is desirably 0.5% by weight or more and 25% by weight or less, preferably 1.0% by weight or more and 15% by weight or less in the electrode mixture. If the composition ratio of the conductive assistant is less than 0.5% by weight, it may be difficult to obtain sufficient conductivity. If the composition ratio exceeds 25% by weight, the positive electrode for a lithium secondary battery that greatly contributes to battery performance. Since the proportion of the active material decreases, problems such as a decrease in discharge capacity may occur.

  As the binder used in the electrode mixture constituting the electrode in the present invention, for example, acrylic resin, polyurethane resin, polyester resin, phenol resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, Examples thereof include cellulose resins such as formaldehyde resin, silicon resin, fluorine resin, and carboxymethyl cellulose, synthetic rubbers such as styrene-butadiene rubber and fluorine rubber, and conductive resins such as polyaniline and polyacetylene. Moreover, the modified body, mixture, or copolymer of these resin may be sufficient.

  Specifically, ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, methacrylic acid, methacrylic ester, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc. Examples thereof include a copolymer contained as a structural unit.

  In particular, the use of a polymer compound having a fluorine atom in the molecule, such as polyvinylidene fluoride, polyvinyl fluoride, and polytetrafluoroethylene, is preferable from the viewpoint of resistance.

  The weight average molecular weight of these resins as a binder is preferably 10,000 to 1,000,000. When the molecular weight is small, the resistance of the binder may decrease. When the molecular weight is increased, the resistance of the binder is improved, but the viscosity of the binder itself is increased, the workability is lowered, and it acts as an aggregating agent.

  A carbon material is most preferable as the conductive additive used in the electrode mixture constituting the electrode in the present invention. The carbon material is not particularly limited as long as it is a conductive carbon material, but graphite, carbon black, carbon nanotube, carbon nanofiber, carbon fiber, fullerene, etc. alone or in combination of two or more. Can be used. From the viewpoint of conductivity, availability, and cost, it is preferable to use carbon black.

  Carbon black is a furnace black produced by continuously pyrolyzing a gas or liquid raw material in a reactor, especially ketjen black using ethylene heavy oil as a raw material. Channel black rapidly cooled and precipitated, thermal black obtained by periodically repeating combustion and thermal decomposition using gas as a raw material, and various types such as acetylene black using acetylene gas as a raw material alone, Or two or more types can be used together. Ordinarily oxidized carbon black, hollow carbon and the like can also be used.

  The oxidation treatment of carbon is performed by treating carbon at a high temperature in the air or by secondary treatment with nitric acid, nitrogen dioxide, ozone, etc., for example, such as phenol group, quinone group, carboxyl group, carbonyl group. This is a treatment for directly introducing (covalently bonding) an oxygen-containing polar functional group to the carbon surface, and is generally performed to improve the dispersibility of carbon. However, since it is common for the conductivity of carbon to fall, so that the introduction amount of a functional group increases, it is preferable to use the carbon which has not been oxidized.

As the specific surface area of the carbon black used increases, the number of contact points between the carbon black particles increases, which is advantageous in reducing the internal resistance of the electrode. Specifically, the BET specific surface area determined from the amount of nitrogen adsorbed by gas adsorption analysis is 20 m ² / g or more and 1500 m ² / g or less, preferably 50 m ² / g or more and 1500 m ² / g or less, more preferably 100 m. It is desirable to use a thing of ² / g or more and 1500 m ² / g or less. When carbon black having a BET specific surface area of less than 20 m ² / g is used, it may be difficult to obtain sufficient conductivity, and carbon black of more than 1500 m ² / g may be difficult to obtain from commercially available materials. There is.

  Moreover, the particle size of the carbon black to be used is preferably 0.005 to 1 μm, and particularly preferably 0.01 to 0.2 μm in terms of primary particle size. However, the primary particle diameter referred to here is an average of particle diameters measured by SEM (scanning electron microscope) or TEM (transmission electron microscope).

Examples of commercially available carbon black include furnace blacks manufactured by Tokai Carbon Corporation such as Toka Black # 4300, # 4400, # 4500, and # 5500;
Furnace Black made by Degussa such as Printex L;
Raven 7000, 5750, 5250, 5000 ULTRA III, 5000 ULT
Furnace black made by Colombian, such as RA, Conductex SC ULTRA, 975 ULTRA, PUER BLACK100, 115, and 205;
# 2350, # 2400B, # 2600B, # 30050B, # 3030B, # 3230B, # 3350B, # 3400B, and # 5400B furnace black manufactured by Mitsubishi Chemical Corporation;
Furnace black from Cabot, such as MONARCH 1400, 1300, 900, Vulcan XC-72R, and Black Pearls 2000;
Furnace black manufactured by TIMCAL, such as Ensaco 250G, Ensaco 260G, Ensaco 350G, and SuperP-Li;
Ketjen Black EC-300J, Akzo Ketjen Black, such as EC-600JD;
Although acetylene black by Denki Kagaku Kogyo Co., Ltd., such as Denka Black, Denka Black HS-100, and FX-35, is mentioned, it is not limited to these.

  The method for producing the electrode is not limited to anything, but for example, a positive electrode active material for a lithium secondary battery according to the present invention, a conductive additive, and a mixture paste in which a binder is dispersed and mixed in a solvent. After adjusting the thickness, it is prepared by coating a current collector such as an aluminum foil and drying.

  When preparing a mixture paste by dispersing and mixing a positive electrode active material for a lithium secondary battery, a conductive additive, and a binder in a solvent, a disperser that is usually used for pigment dispersion or the like can be used.

For example, mixers such as dispersers, homomixers, or planetary mixers;
Homogenizers such as “Clairemix” manufactured by M Technique, or “Fillmix” of PRIMIX;
Media-type dispersers such as paint conditioners (manufactured by Red Devil), ball mills, sand mills (such as “Dynomill” manufactured by Shinmaru Enterprises), attritors, pearl mills (such as “DCP mill” manufactured by Eirich), or coball mills;
Wet jet mill (“Genus PY” manufactured by Genus, “Starburst” manufactured by Sugino Machine, “Nanomizer” manufactured by Nanomizer, etc.) “Claire SS-5” manufactured by M Technique, or “Micros manufactured by Nara Machinery Co., Ltd.” Medialess dispersers such as
Alternatively, other examples include a roll mill, but are not limited thereto. Further, as the disperser, it is preferable to use a disperser that has been subjected to a metal mixing prevention treatment from the disperser.

  For example, when using a media-type disperser, a disperser in which the agitator and vessel are made of a ceramic or resin disperser, or the surface of the metal agitator and vessel is treated with tungsten carbide spraying or resin coating. Is preferably used. And as a medium, it is preferable to use ceramic beads, such as glass beads, zirconia beads, or alumina beads. Moreover, also when using a roll mill, it is preferable to use a ceramic roll. Only one type of dispersion device may be used, or a plurality of types of devices may be used in combination.

  Solvents used in preparing the mixture paste include, for example, alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid Examples include esters, phosphate esters, ethers, nitriles, and water.

  In order to obtain the solubility of the binder resin and the dispersion stability of the carbon material as the conductive auxiliary agent, it is preferable to use a highly polar solvent.

  For example, N-methyl-2-pyrrolidone, an amide solvent obtained by dialkylating nitrogen such as N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, and N, N-diethylacetamide , Hexamethylphosphoric triamide, and dimethyl sulfoxide, but are not limited thereto. Two or more types can be used in combination.

  Next, a lithium secondary battery provided with an electrode using the positive electrode active material for a lithium secondary battery according to the present invention as a positive electrode will be described.

  The lithium secondary battery includes a positive electrode having a positive electrode mixture layer on a current collector, a negative electrode having a negative electrode mixture layer on the current collector, and an electrolyte containing lithium. An electrode base layer may be formed between the positive electrode mixture layer and the current collector or between the negative electrode mixture layer and the current collector.

  For the electrode, the material and shape of the current collector to be used are not particularly limited, and as the material, a metal or an alloy such as aluminum, copper, nickel, titanium, or stainless steel is used. Copper is preferred as the negative electrode material. As the shape, a flat plate foil is generally used, but a roughened surface, a perforated foil shape, and a mesh shape can also be used.

  Examples of the method for forming the electrode underlayer on the current collector include a method in which an electrode base paste in which carbon black as a conductive material and a binder component are dispersed in a solvent is applied to the electrode current collector and dried. The film thickness of the electrode underlayer is not particularly limited as long as the conductivity and adhesion are maintained, but is generally 0.05 μm or more and 20 μm or less, preferably 0.1 μm or more and 10 μm or less. It is.

  As a method of forming an electrode mixture layer on a current collector, a method of directly applying and drying the above-mentioned mixture paste on the current collector, and a mixture paste after forming an electrode base layer on the current collector The method of apply | coating and drying is mentioned. When the electrode mixture layer is formed on the electrode underlayer, after applying the electrode undercoat paste on the current collector, the mixture paste may be applied in a wet state and dried. . The thickness of the electrode mixture layer is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

  There is no restriction | limiting in particular about the coating method, A well-known method can be used. Specific examples include a die coating method, a dip coating method, a roll coating method, a doctor coating method, a spray coating method, a gravure coating method, a screen printing method, and an electrostatic coating method. Moreover, you may perform the rolling process by a lithographic press, a calender roll, etc. after application | coating.

As the electrolytic solution constituting the lithium secondary battery of the present invention, an electrolyte containing lithium is dissolved in a non-aqueous solvent. As electrolytes, LiBF ₄ , LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₃ C , LiI, LiBr, LiCl, LiAlCl, LiHF ₂ , LiSCN, or LiBPh _4, but are not limited thereto.

Although it does not specifically limit as a non-aqueous solvent, For example, carbonates, such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate;
Lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone;
Glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane;
Esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and
Nitriles such as acetonitrile are exemplified. These solvents may be used alone or in combination of two or more.

  Furthermore, the electrolyte solution may be a gelled polymer electrolyte held in a polymer matrix. Examples of the polymer matrix include, but are not limited to, an acrylate resin having a polyalkylene oxide segment, a polyphosphazene resin having a polyalkylene oxide segment, and a polysiloxane having a polyalkylene oxide segment.

  Although the structure of the lithium secondary battery of the present invention is not particularly limited, it is usually composed of a positive electrode and a negative electrode and a separator provided as necessary, and is used as a paper type, a cylindrical type, a button type, a laminated type, etc. It can be made into various shapes according to the purpose.

  EXAMPLES Hereinafter, although this invention is demonstrated in more detail based on an Example, this invention is not limited to an Example. In the examples,% represents% by weight.

The following measuring equipment was used for the analysis of the positive electrode active material for secondary batteries.
-XRD (X-ray diffraction measurement); X'Pert PRO MPD manufactured by PANalytical
CHN elemental analysis; Perkin Elmer 2400 type CHN elemental analysis SEM (scanning electron microscope); Hitachi, Ltd. SEM S-4300
・ TEM (Transmission Electron Microscope): Hitachi High Technology HF2000

<Synthesis of positive electrode active material for lithium secondary battery>
[Example 1; Positive electrode active material for lithium secondary battery (1)]
Transition metal salt hydrate FePO ₄ .2H ₂ O, lithium-containing compound Li ₂ CO ₃ , China rosin X (produced by Arakawa Chemical Industries), a carbon-containing material that produces conductive carbon by thermal decomposition, and reaction FeSO ₄ as an accelerator has a ratio of iron atom content (mol) to lithium atom content (mol) of 1.0, and a ratio of sulfur content (mol) to lithium atom content (mol). Is 3 mol%, and the content of the natural resin in the raw material mixture is weighed to 4.0%, pulverized and mixed with a planetary ball mill, then filled into an alumina crucible, and placed in a nitrogen atmosphere in an electric furnace. And calcination at 700 ° C. for 5 hours to obtain a positive electrode active material (1) for a lithium secondary battery, which is a carbon-coated lithium iron phosphate compound having an olivine structure.
It was confirmed from XRD that the obtained positive electrode active material (1) for lithium secondary batteries was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.8%. Further, SEM and TEM measurements were performed, and the measurement result at 50000 times that of SEM is shown in FIG. 1, and the measurement result at 1200000 times that of TEM is shown in FIG. From the SEM observation, the average primary particle size was 110 nm. Further, from the TEM image, a carbon layer uniformly coated with a thickness of 2 to 3 nm on the surface of the lithium iron phosphate compound particles having an olivine structure was confirmed.

[Example 2: Positive electrode active material for lithium secondary battery (2)]
As a reaction accelerator, other using FeSO ₄ · 7H ₂ O instead of FeSO _4, the same procedure as in Example 1, a lithium secondary battery is a lithium iron phosphate compound having a carbon-coated olivine structure A positive electrode active material (2) was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material (2) for lithium secondary batteries was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.7%.

[Example 3: Positive electrode active material for lithium secondary battery (3)]
As the reaction accelerator, Cu (NO ₃ ) ₂ .3H ₂ O is used instead of FeSO ₄ , and weighed so that the ratio of the nitrogen content (mol) to the lithium atom content (mol) is 3 mol%. In the same manner as in Example 1, a positive electrode active material (3) for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure, was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (3) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.4%.

[Example 4: Positive electrode active material for lithium secondary battery (4)]
The positive electrode active material for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure, as in Example 1, except that CoSO ₄ is used instead of FeSO ₄ as a reaction accelerator (4) was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (4) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.8%.

[Example 5: Positive electrode active material for lithium secondary battery (5)]
As a reaction accelerator, Mn (NO ₃ ) ₂ .6H ₂ O is used instead of FeSO ₄ and weighed so that the ratio of nitrogen content (mol) to lithium atom content (mol) is 3 mol%. In the same manner as in Example 1, a positive electrode active material (5) for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure, was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (5) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.5%.

[Example 6: Positive electrode active material for lithium secondary battery (6)]
A lithium secondary battery which is a lithium iron phosphate compound having a carbon-coated olivine structure in the same manner as in Example 1 except that Fe ₂ (SO ₄ ) ₃ was used instead of FeSO ₄ as a reaction accelerator. A positive electrode active material (6) was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (6) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.6%.

[Example 7: Positive electrode active material for lithium secondary battery (7)]
As a reaction accelerator, (NH ₄ ) ₂ SO ₄ is used instead of FeSO ₄ , and the ratio of the sum of the sulfur content (mol) and the nitrogen content (mol) to the lithium atom content (mol) A positive electrode active material (7) for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure, was obtained in the same manner as in Example 1, except that the amount was 3 mol%. .
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (7) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.7%.

[Example 8: Positive electrode active material for lithium secondary battery (8)]
A positive electrode active material for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure in the same manner as in Example 1 except that FeS was used instead of FeSO ₄ as a reaction accelerator. 8) was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (8) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.3%.

[Example 9: Positive electrode active material for lithium secondary battery (9)]
A positive electrode active material for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure, as in Example 1, except that MgSO ₄ is used instead of FeSO ₄ as a reaction accelerator (9) was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material (9) for lithium secondary batteries was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.6%.

[Example 10: Cathode active material for lithium secondary battery (10)]
A positive electrode active material for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure in the same manner as in Example 1 except that CuS was used instead of FeSO ₄ as a reaction accelerator. 10) was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (10) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.7%.

[Example 11: Positive electrode active material for lithium secondary battery (11)]
In the same manner as in Example 1, except that stearyl alcohol was used in place of Chinese rosin X as a carbon-containing material for producing conductive carbon by thermal decomposition, a lithium iron phosphate compound having a carbon-coated olivine structure was used. A positive electrode active material (11) for a lithium secondary battery was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (11) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.3%.

[Example 12: Positive electrode active material for lithium secondary battery (12)]
Except for using CH ₃ COOLi (lithium acetate) instead of Li ₂ CO ₃ as the lithium-containing compound, the same procedure as in Example 11 was performed. A positive electrode active material (12) for a secondary battery was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (12) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.7%.

[Example 13: Positive electrode active material for lithium secondary battery (13)]
Transition metal salt hydrate Fe ₃ (PO ₄ ) ₂ · 8H ₂ O, lithium-containing compound Li ₃ PO ₄ , stearyl alcohol which is a carbon-containing material that generates conductive carbon by thermal decomposition, and reaction accelerator FeSO ₄ , the ratio of iron atom content (mol) to lithium atom content (mol) is 1.0, and the ratio of sulfur content (mol) to lithium atom content (mol) is 3 mol. %, The stearyl alcohol content in the raw material mixture was weighed to 4.0%, pulverized and mixed with a planetary ball mill, filled in an alumina crucible, and 750 ° C. in a nitrogen atmosphere in an electric furnace. Was fired for 5 hours to obtain a positive electrode active material (13) for a lithium secondary battery, which is a carbon-coated lithium iron phosphate compound having an olivine structure.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (13) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.6%.

[Example 14: Positive electrode active material for lithium secondary battery (14)]
As a reaction accelerator, other using FeSO ₄ · 7H ₂ O instead of FeSO _4, the same procedure as in Example 13, a lithium secondary battery is a lithium iron phosphate compound having a carbon-coated olivine structure A positive electrode active material (14) was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (14) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.3%.

[Example 15: Positive electrode active material for lithium secondary battery (15)]
As in Example 13, except that Cu (NO ₃ ) ₂ .3H ₂ O was used as a reaction accelerator instead of FeSO ₄ and the molar ratio of nitrogen to lithium was 3:97. Then, a positive electrode active material (15) for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure, was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (15) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.2%.

[Example 16: Positive electrode active material for lithium secondary battery (16)]
A positive electrode active material for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure, as in Example 13, except that CoSO ₄ is used instead of FeSO ₄ as a reaction accelerator (16) was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (16) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.6%.

[Example 17: positive electrode active material for lithium secondary battery (17)]
As in Example 13, except that Mn (NO ₃ ) ₂ .6H ₂ O was used as a reaction accelerator instead of FeSO ₄ and the molar ratio of nitrogen and lithium was 3:97. Then, a positive electrode active material (17) for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure, was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (17) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.5%.

[Example 18: Positive electrode active material for lithium secondary battery (18)]
A lithium secondary battery which is a lithium iron phosphate compound having a carbon-coated olivine structure in the same manner as in Example 13 except that Fe ₂ (SO ₄ ) ₃ was used instead of FeSO ₄ as a reaction accelerator. A positive electrode active material (18) was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material (18) for lithium secondary batteries was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.3%.

[Example 19: Positive electrode active material for lithium secondary battery (19)]
As a reaction accelerator, (NH ₄ ) ₂ SO ₄ is used instead of FeSO ₄ , and the ratio of the sum of the sulfur content (mol) and the nitrogen content (mol) to the lithium atom content (mol) A positive electrode active material (19) for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure, was obtained in the same manner as in Example 13 except that the amount was 3 mol%. .
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (19) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.3%.

[Example 20: Positive electrode active material for lithium secondary battery (20)]
A positive electrode active material for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure in the same manner as in Example 13, except that FeS was used instead of FeSO ₄ as a reaction accelerator. 23) was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (20) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.2%.

[Example 21: Positive electrode active material for lithium secondary battery (21)]
The positive electrode active material for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure, as in Example 13, except that MgSO ₄ is used instead of FeSO ₄ as a reaction accelerator (21) was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (21) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.6%.

[Example 22: Cathode active material for lithium secondary battery (22)]
A positive electrode active material for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure in the same manner as in Example 13, except that CuS was used instead of FeSO ₄ as a reaction accelerator. 22) was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (22) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.4%.

[Example 23: Positive electrode active material for lithium secondary battery (23)]
Transition metal salt hydrate Mn (CH ₃ COO) ₂ .4H ₂ O, lithium-containing compound Li ₂ CO ₃ , stearyl alcohol which is a carbon-containing material that generates conductive carbon by thermal decomposition, reaction accelerator Certain FeSO ₄ and niline pentoxide (P ₂ O ₅ ), the ratio of manganese atom content (mol) to lithium atom content (mol) is 1.0, manganese to phosphorus atom content (mol) The ratio of the atomic content (mol) is 1.0, the ratio of the sulfur content (mol) to the lithium atomic content (mol) is 3 mol%, and the stearyl alcohol content in the raw material mixture is 15.0%. And then ground and mixed in a planetary ball mill, filled in an alumina crucible, and baked in an electric furnace at 750 ° C. for 5 hours in a nitrogen atmosphere. Positive active obtain material material (23) for a lithium secondary battery is lithium iron phosphate compound having overturned the olivine structure.
From the XRD, it was confirmed that the obtained positive electrode active material for lithium secondary batteries (23) was a single phase of lithium manganese phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 5.6%.

[Comparative Example 1; Positive electrode active material for lithium secondary battery (a)]
A positive electrode active material (a) for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure, is obtained in the same manner as in Example 1 except that the reaction accelerator FeSO ₄ is not added. It was.
From the XRD, it was confirmed that the obtained positive electrode active material (a) for lithium secondary batteries was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.6%.

[Comparative Example 2; cathode active material for lithium secondary battery (b)]
FePO ₄ .2H ₂ O was filled in an alumina crucible and baked in an electric furnace at 500 ° C. for 10 hours in a nitrogen atmosphere to obtain FePO ₄ anhydride. A positive electrode active material for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure in the same manner as in Comparative Example 1 except that FePO ₄ anhydride is used instead of FePO ₄ .2H ₂ O Material (b) was obtained.
It was confirmed from XRD that the obtained positive electrode active material for lithium secondary battery (b) was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.3%.

[Comparative Example 3; positive electrode active material for lithium secondary battery (c)]
A lithium iron phosphate compound having a carbon-coated olivine structure is the same as in Example 1 except that Fe (C ₂ O ₄ ) · 2H ₂ O is used instead of FeSO ₄ as a reaction accelerator. A positive electrode active material (c) for a lithium secondary battery was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material (c) for lithium secondary batteries was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.9%.

[Comparative Example 4; positive electrode active material (d) for lithium secondary battery]
A positive electrode active material for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure in the same manner as in Example 1 except that FeO was used instead of FeSO ₄ as a reaction accelerator. d) was obtained.
It was confirmed from XRD that the obtained positive electrode active material (d) for lithium secondary batteries was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.4%.

[Comparative Example 5: Positive electrode active material (e) for lithium secondary battery]
A positive electrode active material (e) for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure, is obtained in the same manner as in Example 13, except that the reaction accelerator FeSO ₄ is not added. It was.
It was confirmed from XRD that the obtained positive electrode active material (e) for lithium secondary batteries was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.5%.

[Comparative Example 6; positive electrode active material (f) for lithium secondary battery]
Fe ₃ (PO ₄ ) ₂ · 8H ₂ O was filled in an alumina crucible and baked in an electric furnace at 500 ° C. for 10 hours in a nitrogen atmosphere to obtain an anhydride. A lithium iron phosphate compound having a carbon-coated olivine structure in the same manner as in Comparative Example 13, except that Fe ₃ (PO ₄ ) ₂ anhydride was used instead of Fe ₃ (PO ₄ ) ₂ · 8H ₂ O A positive electrode active material (f) for a lithium secondary battery was obtained.
It was confirmed from XRD that the obtained positive electrode active material (f) for lithium secondary batteries was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 2.5%.

[Comparative Example 7; positive electrode active material for lithium secondary battery (g)]
A positive electrode active material (g) for a lithium secondary battery, which is a lithium iron phosphate compound having a carbon-coated olivine structure, is obtained in the same manner as in Example 23, except that the reaction accelerator FeSO ₄ is not added. It was.
From the XRD, it was confirmed that the obtained positive electrode active material (g) for lithium secondary batteries was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 5.5%.

[Comparative Example 8; cathode active material for lithium secondary battery (h)]
Mn (CH ₃ COO) ₂ .4H ₂ O was filled in an alumina crucible and baked in an electric furnace at 500 ° C. for 10 hours in a nitrogen atmosphere to obtain Mn (CH ₃ COO) ₂ anhydride. A lithium iron phosphate compound having a carbon-coated olivine structure in the same manner as in Comparative Example 13, except that Mn (CH ₃ COO) ₂ anhydride was used instead of Mn (CH ₃ COO) ₂ .4H ₂ O A positive electrode active material (h) for a lithium secondary battery was obtained.
From the XRD, it was confirmed that the obtained positive electrode active material (h) for lithium secondary batteries was a single phase of lithium iron phosphate having an olivine structure. From the CHN elemental analysis, the carbon content was 5.3%.

<Preparation of positive electrode mixture paste for lithium secondary battery>
For the positive electrode active material (1) to (23) and (a) to (h) for the lithium secondary battery, carbon black (Denka Black HS-100; manufactured by Denki Kagaku Kogyo Co., Ltd.), PVDF (polyvinylidene fluoride) (KF polymer W # 1100; manufactured by Kureha) and NMP (N-methyl-2-pyrrolidone) were added and kneaded with a planetary mixer to prepare a positive electrode mixture paste. The solid content composition weight ratio of each positive electrode mixture paste was adjusted as follows.
Positive electrode mixture pastes (1) to (22) and (a) to (g); positive electrode active material / carbon black / PVDF / NMP = 45 / 2.5 / 2.5 / 50.
Positive electrode mixture paste (23) and (h); positive electrode active material / carbon black / PVDF / NMP = 40/5/5/50.

<Preparation of positive electrode for lithium secondary battery>
The positive electrode mixture paste prepared above was applied onto a 20 μm thick aluminum foil serving as a current collector using a doctor blade, then dried by heating under reduced pressure, and subjected to a rolling treatment by a roll press or the like, and a thickness of 50 μm. A positive electrode mixture layer was prepared.

<Assembly of lithium secondary battery positive electrode evaluation cell>
A separator made of a porous polypropylene film between the working electrode and the counter electrode (# 2400, manufactured by Celgard Co., Ltd.) with the positive electrode fabricated previously punched out to a diameter of 9 mm and used as a working electrode and a metal lithium foil (thickness 0.15 mm) as a counter electrode Is inserted and laminated, filled with an electrolyte (nonaqueous electrolyte in which LiPF ₆ is dissolved at a concentration of 1 M in a mixed solvent of ethylene carbonate and diethyl carbonate in a ratio of 1: 1), and a bipolar metal cell (Hosen) (HS flat cell). The cell was assembled in a glove box substituted with argon gas, and after the cell was assembled, predetermined battery characteristics were evaluated.

<Characteristic evaluation of lithium secondary battery positive electrode>
The produced battery evaluation cell was fully charged at a constant current and constant voltage charge (upper limit voltage 4.2 V) at a room temperature (25 ° C.) with a charge rate of 0.2 C, and a discharge lower limit voltage 3 at a constant current at the same rate as the charge. The charge / discharge for discharging to 0.0 V was set to 1 cycle (charge / discharge interval rest time 30 minutes), and this cycle was performed for a total of 20 cycles, and charge / discharge cycle characteristics evaluation (evaluation apparatus: SM-8 manufactured by Hokuto Denko Co., Ltd.) was performed. . The discharge capacity at the 20th cycle was 0.2 C discharge capacity. The evaluation results are shown in Tables 1-3.

  As can be seen from Table 1, in Examples 1 to 12 using the reaction accelerator, the discharge capacity is improved as compared with Comparative Example 1 not using the reaction accelerator of the present invention.

  Thus, when the reaction accelerator of the present invention is used, a high discharge capacity can be obtained by one firing. On the other hand, when a reaction accelerator is not used, as shown in Comparative Example 2, it is necessary to perform a firing step for removing hydrated water from the raw material hydrate, which requires a great deal of energy and time. And the manufacturing cost becomes high.

  Moreover, among Examples 1-12, in the case of Examples 1-5, 11, and 12, the tendency for higher discharge capacity to be obtained was seen.

  Like Table 1, also in Table 2, Examples 13-22 using the reaction accelerator have improved discharge capacity compared with Comparative Example 5 not using the reaction accelerator of the present invention. According to the production method of the invention, it can be seen that a high discharge capacity can be obtained without performing the firing step as shown in Comparative Example 6.

As in Tables 1 and 2, also in Table 3, Example 23 using the reaction accelerator has an improved discharge capacity compared to Comparative Example 7 not using the reaction accelerator of the present invention. According to the manufacturing method of the invention, it is understood that a high discharge capacity can be obtained without performing the firing step as shown in Comparative Example 8.

Claims (5)

A lithium-containing compound, a lithium secondary comprising a transition metal salt sum thereof, to obtain mixed to the mixture and a reaction accelerator and (A), and a step (B) for calcining the mixture at 300 ° C. or higher 900 ° C. or less A method for producing a positive electrode active material for a secondary battery , comprising:
The transition metal _{hydrate, FePO 4 · 2H 2 O,} Fe 3 (PO 4) is ₂ · 8H ₂ O or _{Mn (CH 3 COO) 2 ·} 4H 2 O,
The reaction accelerator is a sulfate, nitrate or sulfide containing M ² or a hydrate thereof [wherein M ² is Fe (II), Co (II), Mn (II), Cu (II) , Mg (II), Fe (III) or NH ₄ (I). ]
A method for producing a positive electrode active material for a lithium secondary battery . Reaction accelerators, positive electrode active material manufacturing method for a lithium secondary battery of thermal decomposition according to claim 1, wherein at 900 ° C. or less. The reaction accelerator is a sulfate or nitrate containing M ² or a hydrate thereof [provided that M ² is selected from Fe (II), Co (II), Mn (II ) or Cu (II) 1 type or 2 types or more. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1 or 2 . The method for producing a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 3 , wherein the transition metal salt hydrate is FePO ₄ · 2H ₂ O. The method for producing a positive electrode active material for a lithium secondary battery according to any one of claims 1 to 4, wherein a carbon-containing material that generates conductive carbon by thermal decomposition is further added in the step (A).

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