JP6322730B1 - Positive electrode active material for lithium ion secondary battery and method for producing the same - Google Patents

Abstract

A positive electrode active material composite for a lithium ion secondary battery useful as a positive electrode active material capable of obtaining a lithium ion secondary battery having a high charge / discharge capacity while using a lithium phosphate compound, and its production Provide a method. Lithium phosphate compound particles represented by the following formula (I): LiFeaMnbMgCodM1ePO4 (I), and lithium silicate system represented by the following formula (II): Li2FefMngCohAliM2jSiO4 (II) Mass of the content of the lithium phosphate compound particles represented by the above formula (I) and the content of the lithium silicate compound particles represented by the above formula (II) The positive electrode active material composite for a lithium ion secondary battery having a ratio ((I) :( II)) of more than 50:50 and 95: 5 or less. [Selection figure] None

Description

  The present invention relates to a positive electrode active material composite for a lithium ion secondary battery that can effectively increase the charge / discharge capacity in the lithium ion secondary battery, and a method for producing the same.

  A secondary battery such as a lithium ion secondary battery is a kind of non-aqueous electrolyte battery, and is used in a wide range of fields such as mobile phones, digital cameras, notebook PCs, hybrid cars, and electric cars. Lithium ion secondary batteries mainly use lithium metal oxide as a positive electrode material and a carbon material such as graphite as a negative electrode material.

There are many known positive electrode materials such as lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMnO ₂ ), lithium iron phosphate (LiFePO ₄ ), and lithium iron silicate (Li ₂ FeSiO ₄ ). Yes. In particular, lithium phosphate compounds such as Li (Fe, Mn) PO ₄ having an olivine structure are not greatly affected by resource restrictions, and can exhibit high safety. It is a positive electrode material useful for obtaining a lithium ion secondary battery having excellent physical properties, and various developments have heretofore been made.

  For example, in Patent Document 1, an attempt is made to improve the performance of the obtained battery by making primary crystal particles ultrafine particles and shortening the lithium ion diffusion distance in the olivine-type positive electrode active material. In Patent Document 2, a conductive carbonaceous material is uniformly deposited on the particle surface of the positive electrode active material, and a regular electric field distribution is obtained on the particle surface to increase the output of the battery.

JP 2010-251302 A JP 2001-15111 A

  However, these positive electrode active materials are mainly caused by the use of lithium phosphate compounds, and although the remaining battery properties are excellent, there is still a possibility that the charge / discharge capacity cannot be sufficiently increased. It is expensive and further improvement is required.

  Accordingly, an object of the present invention is to provide a positive electrode active material for a lithium ion secondary battery that is useful as a positive electrode active material and that can provide a lithium ion secondary battery having a high charge / discharge capacity while using a lithium phosphate compound. It is providing the composite_body | complex and its manufacturing method.

  Therefore, the present inventors have made various studies, and while using mainly a lithium phosphate compound, a composite comprising lithium phosphate compound particles and lithium silicate compound particles is supported. In the obtained lithium ion battery, it discovered that charging / discharging capacity could be increased effectively, and came to complete this invention.

That is, the present invention provides the following formula (I):
LiFe _a Mn _b Mg _c Co _d M ¹ _e PO ₄ (I)
(In formula (I), M ¹ represents Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. A, b, c, d, and e are 0. ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 1, 0 ≦ d ≦ 1, 0 ≦ e ≦ 0.2, and 2 × (a + b + c + d) + (valence of M ¹ ) × e = 2 And a number satisfying and a + b + c + d ≠ 0.)
Lithium phosphate compound particles represented by the following formula (II):
_{Li 2 Fe f Mn g Co h} Al i M 2 j SiO 4 ··· (II)
(In the formula (II), M ² represents Ni, Zn, V or Zr. F, g, h, i and j are 0 ≦ f ≦ 1, 0 ≦ g ≦ 1, 0 ≦ h ≦ 1, 0. ≦ i ≦ 1, 0 ≦ j <1, and 2 × (f + g + h) + 3 × i + (valence of M ² ) × j = 2 and a number satisfying f + g + h + i ≠ 0 is shown.
The lithium silicate compound particles represented by the formula (I) and the lithium silicate compound particles represented by the formula (II) Provided is a positive electrode active material composite for a lithium ion secondary battery having a mass ratio ((I) :( II)) of more than 50:50 and not more than 95: 5 with respect to the content of compound particles.

  The present invention also mixes lithium phosphate compound particles represented by the above formula (I) and lithium silicate compound particles represented by the above formula (II) while applying compressive force and shear force. The manufacturing method of the said positive electrode active material composite_body | complex for lithium ion secondary batteries provided with process (X) to process is provided.

  According to the positive electrode active material composite for a lithium ion secondary battery of the present invention, in a lithium ion battery obtained by using this as a positive electrode active material, a sufficient charge / discharge capacity is achieved while using a lithium phosphate compound. It is possible to enhance the battery physical properties.

Hereinafter, the present invention will be described in detail.
The positive electrode active material composite for a lithium ion secondary battery of the present invention has the following formula (I):
LiFe _a Mn _b Mg _c Co _d M ¹ _e PO ₄ (I)
(In formula (I), M ¹ represents Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. A, b, c, d, and e are 0. ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 1, 0 ≦ d ≦ 1, 0 ≦ e ≦ 0.2, and 2 × (a + b + c + d) + (valence of M ¹ ) × e = 2 And a number satisfying and a + b + c + d ≠ 0.)
Lithium phosphate compound particles represented by the following formula (II):
_{Li 2 Fe f Mn g Co h} Al i M 2 j SiO 4 ··· (II)
(In the formula (II), M ² represents Ni, Zn, V or Zr. F, g, h, i and j are 0 ≦ f ≦ 1, 0 ≦ g ≦ 1, 0 ≦ h ≦ 1, 0. ≦ i ≦ 1, 0 ≦ j <1, and 2 × (f + g + h) + 3 × i + (valence of M ² ) × j = 2 and a number satisfying f + g + h + i ≠ 0 is shown.
These are particles formed by supporting lithium silicate compound particles represented by

  The lithium phosphate compound particles represented by the above formula (I) and the lithium silicate compound particles represented by the above formula (II) are both particles having an olivine structure. The former lithium phosphate compound particles include at least one of transition metals of iron, manganese, magnesium, and cobalt, and the latter lithium silicate compound particles include at least one of iron, manganese, cobalt, and aluminum. The positive electrode active material composite for a lithium ion secondary battery of the present invention containing a metal is a useful positive electrode active material for a lithium ion secondary battery formed by supporting these particles.

In the above formula (I), M ¹ represents Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd, preferably Mg, Zr, or Mo. a, b, c, and d are 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 1, 0 ≦ d ≦ 1, preferably 0.05 ≦ a ≦ 0.95, 0. 01 ≦ b ≦ 1, 0 ≦ c ≦ 0.1, 0 ≦ d ≦ 0.1, more preferably 0.1 ≦ a ≦ 0.9, 0.1 ≦ b ≦ 1, 0 ≦ c ≦ 0 .05, 0 ≦ d ≦ 0.05. e is 0 ≦ e ≦ 0.2, and preferably 0 ≦ e <0.1. A, b, c, d and e are numbers satisfying 2 × (a + b + c + d) + (valence of M ¹ ) × e = 2 and satisfying a + b + c + d ≠ 0.
Specific examples of the lithium phosphate compound represented by the above formula (I) include LiFe _0.9 Mn _0.1 PO ₄ , LiFe _0.2 Mn _0.8 PO ₄ , LiFe _0.15 Mn _0.75 Mg _0.1 PO ₄ , and LiFe _0.19 Mn _0.75. Zr _0.03 PO _{4 and the} like can be mentioned, among which LiFe _0.2 Mn _0.8 PO ₄ is preferable.

The average particle diameter of the lithium phosphate compound represented by the above formula (I) is preferably 30 to 800 nm, more preferably 40 to 500 nm. Moreover, the lithium phosphate represented by the above formula (I) The tap density of the system compound is preferably 0.4 to 1.5 g / cm ³ , more preferably 0.5 to 1.4 g / cm ³ .
The tap density is obtained by mechanically tapping a measurement container containing a sample m (g) having a known weight and reading the sample volume V (cm ³ ) when no volume change is recognized. The average value calculated | required from the value calculated using m / V is meant.

In the above formula (II), M ² represents Ni, Zn, V or Zr, preferably V or Zr, more preferably Zr. f, g, h, and i are 0 ≦ f ≦ 1, 0 ≦ g ≦ 1, 0 ≦ h ≦ 1, 0 ≦ i ≦ 1, preferably 0.01 ≦ f ≦ 0.99, 0. 01 ≦ g ≦ 0.99, 0 ≦ h ≦ 0.3, 0 ≦ i ≦ 0.3, more preferably 0.1 ≦ f ≦ 0.9, 0.1 ≦ g ≦ 0.9, 0 ≦ h ≦ 0.15 and 0 ≦ i ≦ 0.15. j is 0 ≦ j <1, and preferably 0 <j <0.2. These f, g, h, i and j are numbers satisfying 2 × (f + g + h) + 3 × i + (valence of M ² ) × j = 2 and satisfying f + g + h + i ≠ 0.
Specific examples of the polyanion material particles represented by the above formula (II) include Li ₂ Fe _0.45 Mn _0.45 Co _0.1 SiO ₄ , Li ₂ Fe _0.36 Mn _0.54 Al _0.066 SiO ₄ , Li ₂ Fe _0.45 Mn _0.45 Zn _Examples include _0.1 SiO ₄ , Li ₂ Fe _0.36 Mn _0.54 V _0.066 SiO ₄ , and Li ₂ Fe _0.282 Mn _0.658 Zr _0.02 SiO _4. Among them, Li ₂ Fe _0.282 Mn _0.658 Zr _0.02 SiO ₄ is preferable.

The average particle size of the lithium silicate compound particles represented by the above formula (II) is preferably 10 to 150 nm, more preferably 10 to 120 nm. The tap density of the lithium silicate compound particles represented by the above formula (II) is preferably 0.4 to 1.5 g / cm ³ , more preferably 0.5 to 1.4 g / cm ^3. It is.

  The mass ratio ((I) :( II)) of the content of the lithium phosphate compound represented by the above formula (I) and the content of the lithium silicate compound particles represented by the above formula (II) is 50:50 and 95: 5 or less, preferably 55:45 to 90:10, more preferably 60:40 to 85:15, and even more preferably 65:35 to 80:20. . The positive electrode active material composite for a lithium ion secondary battery of the present invention has a plurality of lithium phosphate compounds represented by the above formula (I) and a plurality of the above formulas (II) while maintaining such a mass ratio. Are particles that are firmly supported while aggregating with each other. The composite having such a structure allows the lithium phosphate compound represented by the above formula (I) and the lithium silicate compound particles represented by the above formula (II) to act synergistically. Thus, when a lithium ion secondary battery is constructed, the charge / discharge capacity can be remarkably improved as compared with the case of using a positive electrode active material composed only of a lithium phosphate compound.

  The content of the lithium phosphate compound represented by the above formula (I) is preferably more than 50% by mass and 94% by mass or less in the positive electrode active material composite for a lithium ion secondary battery of the present invention, More preferably, it is 55-89 mass%, More preferably, it is 60-84 mass%. Further, the content of the lithium silicate compound particles represented by the above formula (II) is preferably more than 6% by mass and less than 50% by mass in the positive electrode active material composite for a lithium ion secondary battery of the present invention. More preferably, it is 11-45 mass%, More preferably, it is 16-40 mass%.

  The lithium phosphate compound represented by the above formula (I) and the lithium silicate compound particles represented by the above formula (II) are represented by the above formula (I) from the viewpoint of improving charge / discharge capacity. It is preferable that carbon derived from cellulose nanofibers or carbon derived from a water-soluble carbon material is supported on the particle surface of the polyanion material or both particle surfaces.

  The cellulose nanofiber as the carbon source is a skeletal component that occupies about 50% of all plant cell walls, and can be obtained by defibrating the plant fibers constituting such cell walls to nano size. Carbon, which is a strength fiber and derived from cellulose nanofibers, has a periodic structure. The fiber diameter of the cellulose nanofiber is 1 nm to 100 nm, and has good dispersibility in water. Further, in the cellulose molecular chain constituting the cellulose nanofiber, since a periodic structure is formed by carbon, this is carbonized together with the inorganic compound and is firmly supported on the particle surfaces of both lithium compounds. Thus, a useful positive electrode active material composite for a lithium ion secondary battery capable of improving the charge / discharge capacity can be obtained.

  The water-soluble carbon material as the carbon source means a carbon material that dissolves in 100 g of water at 25 ° C. in an amount equivalent to carbon atom of the water-soluble carbon material of 0.4 g or more, preferably 1.0 g or more. Therefore, it is present on the surface of the lithium compound particles as carbon. Examples of the water-soluble carbon material include one or more selected from saccharides, polyols, polyethers, and organic acids. More specifically, for example, monosaccharides such as glucose, fructose, galactose and mannose; disaccharides such as maltose, sucrose and cellobiose; polysaccharides such as starch and dextrin; ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol and butane Examples include polyols and polyethers such as diol, propanediol, polyvinyl alcohol, and glycerin; and organic acids such as citric acid, tartaric acid, and ascorbic acid. Among these, glucose, fructose, sucrose, and dextrin are preferable, and glucose is more preferable from the viewpoint of improving the solubility and dispersibility in a solvent and effectively functioning as a carbon material.

The amount of carbon supported on the surface of the lithium phosphate compound particles represented by the formula (I) or the surface of the lithium silicate compound particles represented by the formula (II) is the carbon source. It corresponds to the carbon atom equivalent amount of the water-soluble carbon material. The amount of carbon supported (atomic equivalent amount of carbon derived from the water-soluble carbon material) is the lithium phosphate compound particle represented by the above formula (I) or the lithium silicate compound represented by the above formula (II). In the particles, it is preferably 0.3 to 20% by mass, more preferably 0.4 to 15% by mass, and still more preferably 0.5 to 10% by mass.
In addition, the carbon atom conversion amount (carbon loading amount) of the water-soluble carbon material present in the lithium compound particles can be confirmed as the carbon amount measured using a carbon / sulfur analyzer.

The lithium phosphate compound particles represented by the above formula (I) or the lithium silicate compound particles represented by the above formula (II) are prepared by adding a phosphate compound or a silicate compound to a mixture A containing a lithium compound. Mixing to obtain complex A (A),
The obtained complex A and a metal salt containing at least one of an iron compound, a manganese compound, a magnesium compound, or a cobalt compound, or a metal containing at least one of an iron compound, a manganese compound, a cobalt compound, or an aluminum compound Step (B) of obtaining slurry B by subjecting slurry water B containing salt to a hydrothermal reaction, and step (C) of firing obtained composite B
The lithium phosphate compound particles represented by the formula (I) and the lithium silicate compound particles represented by the formula (II) can be obtained independently from each other. To obtain as separate and independent particles.
That is, when obtaining the lithium phosphate compound particles represented by the above formula (I), the phosphate compound is used in the step (A), and the lithium silicate compound particles represented by the above formula (II) are used. When obtaining, a silicic acid compound may be used in the step (A). Moreover, when carrying | supporting carbon derived from cellulose nanofiber or carbon derived from a water-soluble carbon material on the surface of these polyanion material particles, the cellulose nanofiber or the water-soluble carbon material is used in the step (A) or the step (B). What is necessary is just to add.

The step (A) is a step of obtaining the composite A by mixing the phosphoric acid compound or the silicic acid compound with the mixture A containing the lithium compound.
Examples of lithium compounds that can be used include hydroxides (for example, LiOH.H ₂ O), carbonates, sulfates, and acetates. Of these, hydroxide is preferable.
The content of the lithium compound in the mixture A is preferably 5 to 50 parts by mass, more preferably 7 to 45 parts by mass with respect to 100 parts by mass of water. More specifically, when a phosphoric acid compound is used in the step (A), the content of the lithium compound in the mixture A is preferably 5 to 50 parts by mass, more preferably 10 to 100 parts by mass of water. -45 parts by mass. Moreover, when a silicic acid compound is used, the content of the silicic acid compound in the mixture A is preferably 5 to 40 parts by mass, more preferably 7 to 35 parts by mass with respect to 100 parts by mass of water.

  Before mixing the phosphoric acid compound or the silicic acid compound with the mixture A, it is preferable to stir the mixture A in advance. The stirring time of the mixture A is preferably 1 to 15 minutes, more preferably 3 to 10 minutes. Moreover, the temperature of the mixture A becomes like this. Preferably it is 20-90 degreeC, More preferably, it is 20-70 degreeC.

Examples of the phosphoric acid compound used in the step (A) include orthophosphoric acid (H ₃ PO ₄ , phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, and ammonium hydrogen phosphate. . Of these, phosphoric acid is preferably used, and is preferably used as an aqueous solution having a concentration of 70 to 90% by mass. In the step (A), when phosphoric acid is mixed with the mixture A, it is preferable to add phosphoric acid dropwise while stirring the mixture A. By adding phosphoric acid dropwise to the mixture A and adding it little by little, the reaction proceeds well in the mixture A, and the composite A is generated while being uniformly dispersed in the slurry, and the composite A is agglomerated unnecessarily. It can also be effectively suppressed.

The dropping rate of phosphoric acid into the mixture A is preferably 15 to 50 mL / min, more preferably 20 to 45 mL / min, and further preferably 28 to 40 mL / min. Moreover, the stirring time of the mixture A while dropping phosphoric acid is preferably 0.5 to 24 hours, and more preferably 3 to 12 hours. Furthermore, the stirring speed of the mixture A while dropping phosphoric acid is preferably 200 to 700 rpm, more preferably 250 to 600 rpm, and further preferably 300 to 500 rpm.
In addition, when stirring the mixture A, it is preferable to further cool to the boiling point temperature of the mixture A or lower. Specifically, cooling to 80 ° C. or lower is preferable, and cooling to 20 to 60 ° C. is more preferable.

The silicic acid compound used in the step (A) is not particularly limited as long as it is a reactive silica compound, and examples thereof include amorphous silica, Na ₄ SiO ₄ (for example, Na ₄ SiO ₄ .H ₂ O), and the like. .

The mixture A after mixing the phosphoric acid compound or silicic acid compound preferably contains 2.0 to 4.0 moles of lithium with respect to 1 mole of phosphoric acid or silicic acid, and 2.0 to 3.1 moles. The lithium compound and the phosphoric acid compound or silicic acid compound may be used so that the amount is more preferable. More specifically, when a phosphoric acid compound is used in step (A), the mixture A after mixing the phosphoric acid compound contains 2.7 to 3.3 mol of lithium with respect to 1 mol of phosphoric acid. Of these, 2.8 to 3.1 mol is more preferable. When a silicic acid compound is used in the step (A), the mixture A after mixing the silicic acid compound preferably contains 2.0 to 4.0 mol of lithium with respect to 1 mol of silicic acid. It is more preferable to contain 0-3.0.
What is necessary is just to use the said lithium compound and a phosphoric acid compound or a silicic acid compound so that it may become such quantity.

  Lithium phosphate compound particles represented by the above formula (I) are obtained by purging the mixture A after mixing the phosphoric acid compound or silicic acid compound with nitrogen to complete the reaction in the mixture. Alternatively, the composite A that is a precursor of the lithium silicate compound particles represented by the above formula (II) is formed in the mixture. When nitrogen is purged, the reaction can proceed in a state where the dissolved oxygen concentration in the mixture A is reduced, and the dissolved oxygen concentration in the resulting mixture containing the complex A is also effectively reduced. Therefore, oxidation of the iron compound or manganese compound added in the next step can be suppressed. In the mixture containing the composite A, the lithium phosphate compound particles represented by the above formula (I) or the precursor of the lithium silicate compound particles represented by the above formula (II) are finely dispersed. Present as particles.

The pressure for purging nitrogen is preferably 0.1 to 0.2 MPa, more preferably 0.1 to 0.15 MPa. Moreover, the temperature of the mixture A after mixing a phosphoric acid compound or a silicic acid compound becomes like this. Preferably it is 20-80 degreeC, More preferably, it is 20-60 degreeC.
Moreover, when purging nitrogen, it is preferable to stir the mixture A after mixing a phosphoric acid compound or a silicic acid compound from a viewpoint of making reaction progress favorable. The stirring speed at this time is preferably 200 to 700 rpm, more preferably 250 to 600 rpm.

  Further, from the viewpoint of more effectively suppressing the oxidation of the composite A on the surface of the dispersed particles and miniaturizing the dispersed particles, the dissolved oxygen concentration in the mixture A after mixing the phosphate compound or the silicate compound is set to 0. 0.5 mg / L or less is preferable, and 0.2 mg / L or less is more preferable.

  In the step (B), the complex A obtained in the step (A) and at least a metal salt containing any one of an iron compound, a manganese compound, a magnesium compound, and a cobalt compound, or at least an iron compound, a manganese compound, and cobalt In this step, slurry water B containing a metal salt containing either a compound or an aluminum compound is subjected to a hydrothermal reaction to obtain composite B. The composite A obtained by the step (A) is a mixture of the lithium phosphate compound particles represented by the formula (I) or the lithium silicate compound particles represented by the formula (II). A metal salt containing at least one of an iron compound, a manganese compound, a magnesium compound, or a cobalt compound is added to the precursor of the lithium phosphate compound particles represented by the above formula (I). A metal salt containing at least one of an iron compound, a manganese compound, a cobalt compound, or an aluminum compound is added to the precursor of the lithium silicate compound particles represented by the above formula (II), and slurry water is added. It is preferable to use as B. As a result, the lithium phosphate compound particles represented by the above formula (I) or the lithium silicate compound particles represented by the above formula (II) become very fine, and the particles are firmly dispersed while being effectively dispersed. When the resulting positive electrode active material composite for a lithium ion secondary battery is used as a positive electrode for a lithium ion secondary battery, an excellent charge / discharge capacity can be exhibited.

Examples of iron compounds that can be used include iron acetate, iron nitrate, iron sulfate, and hydrates thereof. These may be used alone or in combination of two or more. Among these, iron sulfate is preferable from the viewpoint of improving battery characteristics.
Examples of manganese compounds that can be used include manganese acetate, manganese nitrate, manganese sulfate, and hydrates thereof. These may be used alone or in combination of two or more. Among these, manganese sulfate is preferable from the viewpoint of improving battery characteristics.
Examples of the cobalt compound that can be used include cobalt acetate, cobalt nitrate, cobalt sulfate, and hydrates thereof. These may be used alone or in combination of two or more. Of these, cobalt sulfate is preferable from the viewpoint of improving battery characteristics.
Examples of the aluminum compound that can be used include aluminum acetate, aluminum nitrate, aluminum sulfate, and hydrates thereof. These may be used alone or in combination of two or more. Among these, aluminum sulfate is preferable from the viewpoint of improving battery characteristics.
Examples of magnesium compounds that can be used include magnesium acetate, magnesium nitrate, magnesium sulfate, and hydrates thereof. These may be used alone or in combination of two or more. Among these, magnesium sulfate is preferable from the viewpoint of improving battery characteristics.

  For example, when both an iron compound and a manganese compound are used as the metal salt, the molar ratio of the manganese compound and the iron compound used (manganese compound: iron compound) is preferably 99: 1 to 1:99, more preferably Is 90: 10-10: 90.

Furthermore, if necessary, a metal (M ¹ or M ² ) salt other than the above may be used as the metal salt. Metal (M ^1, or M ²⁾ M ¹ in the salts, and M ² has the same meaning as M ^1, or M ² in the formula (I) or above-mentioned formula (II), as such a metal salt, sulfate , Halogen compounds, organic acid salts, and hydrates thereof can be used. These may be used alone or in combination of two or more. Among them, it is more preferable to use a sulfate from the viewpoint of improving battery physical properties.
When these metal (M ¹ or M ² ) salts are used, the total amount of iron compound, manganese compound, cobalt compound, aluminum compound, magnesium compound, and metal (M ¹ or M ² ) salt added is It is preferably 0.99 to 1.01 mol, more preferably 0.995 to 1.005 mol, per 1 mol of phosphoric acid or silicic acid in the mixture obtained in A).

  The amount of water used for the hydrothermal reaction is phosphoric acid or silicate ions contained in the slurry water B from the viewpoint of the solubility of the metal salt used, the ease of stirring, the efficiency of synthesis, etc. Preferably it is 10-50 mol with respect to 1 mol, More preferably, it is 12.5-45 mol. More specifically, the amount of water used for the hydrothermal reaction is preferably 10 to 30 mol, more preferably 12 when the ions contained in the slurry water B are phosphate ions. .5 to 25 moles. Moreover, when the ion contained in the slurry water B is a silicate ion, Preferably it is 10-50 mol, More preferably, it is 12.5-45 mol.

In the step (B), the order of adding the metal salts is not particularly limited. Moreover, while adding these metal salts, you may add antioxidant as needed. As such an antioxidant, sodium sulfite (Na ₂ SO ₃ ), sodium hydrosulfite (Na ₂ S ₂ O ₄ ), aqueous ammonia and the like can be used. The addition amount of the antioxidant is excessively added, thereby generating lithium phosphate compound particles represented by the above formula (I) or lithium silicate compound particles represented by the above formula (II). From the viewpoint of preventing suppression, it is preferably 0.01 to 1 mol, more preferably 0.03 to 0.5 mol, relative to a total of 1 mol of all metal salts used.

  The content of the complex B in the slurry water B obtained by adding the metal salt or the antioxidant is preferably 10 to 50% by mass, more preferably 15 to 45% by mass, and still more preferably. Is 20-40 mass%.

The hydrothermal reaction in a process (B) should just be 100 degreeC or more, and 130-180 degreeC is preferable. The hydrothermal reaction is preferably carried out in a pressure vessel, and when the reaction is carried out at 130 to 180 ° C, the pressure at this time is preferably 0.3 to 0.9 MPa, and the reaction is carried out at 140 to 160 ° C. The pressure is preferably 0.3 to 0.6 MPa. The hydrothermal reaction time is preferably 0.1 to 48 hours, more preferably 0.2 to 24 hours.
The obtained composite B is a granular composite containing the lithium phosphate compound particles represented by the above formula (I) or the lithium silicate compound particles represented by the above formula (II). This can be isolated by washing with water after filtration and drying. As the drying means, freeze drying or vacuum drying is used.

  Step (C) is a step of firing the obtained composite B. In the step (A) or the step (B), when cellulose nanofiber or a water-soluble carbon material is added, the firing is performed in a reducing atmosphere or an inert atmosphere. When the cellulose nanofiber or the water-soluble carbon material is used as the carbon source, the firing temperature is preferably 500 to 800 ° C, more preferably 600 to 770 ° C from the viewpoint of carbonizing the cellulose nanofiber more effectively. More preferably, it is 650-750 degreeC. The firing time is preferably 10 minutes to 3 hours, more preferably 30 minutes to 1.5 hours.

The positive electrode active material composite for a lithium ion secondary battery of the present invention comprises a lithium phosphate compound particle represented by the above formula (I) and a lithium silicate compound particle represented by the above formula (II). The average particle size of the positive electrode active material composite for a lithium ion secondary battery is preferably 1 to 100 μm, more preferably 5 to 50 μm. Moreover, the tap density of the positive electrode active material composite for a lithium ion secondary battery of the present invention is preferably 0.5 to 2.5 g / cm ³ , more preferably 1.5 to 2.5 g / cm ³ . is there. Further, BET specific surface area of the positive electrode active material composite for a lithium ion secondary battery of the present invention, from the viewpoint of improving the charge-discharge capacity, preferably 5 to 40 m ² / g, more preferably 7~30m ² / g.

  The positive electrode active material composite for a lithium ion secondary battery of the present invention may have a particle surface on which carbon derived from a water-insoluble conductive carbon material other than cellulose nanofibers is supported. Lithium phosphate compound represented by the above formula (I), which is supported not only on the particle surface of the positive electrode active material composite for a lithium ion secondary battery but also agglomerated and supported on each other by supporting the carbon. Carbon can also be interspersed or interspersed between the particles and the lithium silicate compound particles represented by the above formula (II), and when this is used as a positive electrode for a lithium ion secondary battery, battery performance is further improved. It can raise and it can contribute to the improvement of charging / discharging capacity.

  The water-insoluble conductive carbon material as the carbon source is a water-insoluble carbon material whose dissolution amount in 100 g of water at 25 ° C. is less than 0.4 g in terms of carbon atom of the water-insoluble conductive carbon material. It is a carbon source other than cellulose nanofibers, and is itself a carbon source having electrical conductivity without reduction firing. Examples of the water-insoluble conductive carbon material include one or more selected from graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. The graphite may be any of artificial graphite (scaly, massive, earthy, graphene) or natural graphite.

The BET specific surface area of the water-insoluble conductive carbon material other than the cellulose nanofiber is preferably 1 to 750 m ² / g, more preferably 3 to 500 m ² / g, from the viewpoint of effectively increasing the charge / discharge capacity. is there. Moreover, from the same viewpoint, the average particle diameter of the water-insoluble conductive carbon material other than the cellulose nanofiber is preferably 0.5 to 20 μm, and more preferably 1.0 to 15 μm.

The amount of carbon in terms of carbon derived from the water-insoluble conductive carbon material other than the cellulose nanofiber (the amount of carbon supported) is preferably 1 to 15 mass in the positive electrode active material composite for a lithium ion secondary battery of the present invention. %, More preferably 2 to 12% by mass, and even more preferably 3 to 10% by mass.
In addition, the atomic conversion amount of carbon (carbon loading) of the water-insoluble conductive carbon material other than the cellulose nanofibers present in the positive electrode active material composite for lithium ion secondary battery is determined using a carbon / sulfur analyzer. It can confirm as the measured carbon amount.

Specific examples of the positive electrode active material composite for a lithium ion secondary battery of the present invention include the following.
(1) Lithium phosphate compound particles represented by the above formula (I) (supporting carbon derived from cellulose nanofibers and water-soluble carbon material) and silicic acid represented by the above formula (II) A positive electrode active material composite for a lithium ion secondary battery in which lithium compound particles (with carbon from cellulose nanofibers and carbon from a water-soluble carbon material) are supported at the predetermined mass ratio,
(2) Lithium phosphate compound particles represented by the above formula (I) (without supporting carbon derived from cellulose nanofibers and water-soluble carbon material) and silicic acid represented by the above formula (II) Particles of a positive electrode active material composite for a lithium ion secondary battery comprising lithium-based compound particles (no support of carbon derived from cellulose nanofibers and no carbon derived from a water-soluble carbon material) at the predetermined mass ratio. A positive electrode active material composite for a lithium ion secondary battery comprising carbon derived from a water-insoluble conductive carbon material other than cellulose nanofibers on the surface;
(3) Lithium phosphate compound particles represented by the above formula (I) (supporting carbon derived from cellulose nanofibers and water-soluble carbon material) and silicic acid represented by the above formula (II) A positive electrode active material composite for a lithium ion secondary battery in which lithium-based compound particles (without supporting carbon derived from cellulose nanofibers and carbon derived from a water-soluble carbon material) are supported at the predetermined mass ratio;
(4) Lithium phosphate compound particles represented by the above formula (I) (supporting carbon derived from cellulose nanofibers and water-soluble carbon material) and silicic acid represented by the above formula (II) Particles of a positive electrode active material composite for a lithium ion secondary battery comprising lithium-based compound particles (no support of carbon derived from cellulose nanofibers and no carbon derived from a water-soluble carbon material) at the predetermined mass ratio. A positive electrode active material composite for a lithium ion secondary battery comprising carbon derived from a water-insoluble conductive carbon material other than cellulose nanofibers on the surface;
(5) Lithium phosphate compound particles represented by the above formula (I) (supporting carbon derived from cellulose nanofibers and water-soluble carbon material) and silicic acid represented by the above formula (II) Lithium compound particles (with carbon from cellulose nanofibers and carbon from water-soluble carbon material) supported at the predetermined mass ratio, and particles of positive electrode active material composite for lithium ion secondary battery A positive electrode active material composite for a lithium ion secondary battery, on the surface of which carbon derived from a water-insoluble conductive carbon material other than cellulose nanofibers is supported.

  Among these aspects of the positive electrode active material composites (1) to (5) for lithium ion secondary batteries, from the viewpoint of improving the cycle characteristics of the lithium ion secondary battery efficiently and effectively, the lithium ion secondary battery The embodiment of the positive electrode active material composite (5) for a battery is preferable.

  The positive electrode active material composite for a lithium ion secondary battery of the present invention comprises a lithium phosphate compound particle represented by the above formula (I) and a lithium silicate compound particle represented by the above formula (II), It can be obtained by a production method comprising a step (X) of mixing treatment while applying a compressive force and a shearing force.

  Specifically, in the step (X), after mixing the lithium phosphate compound particles represented by the above formula (I) and the lithium silicate compound particles represented by the above formula (II), the compression force and The step of mixing while applying a shearing force is preferred. As a result, the lithium phosphate compound particles represented by the above formula (I) and the lithium silicate compound particles represented by the above formula (II) can be supported while firmly agglomerated while being uniformly dispersed. And a positive electrode active material composite for a lithium ion secondary battery useful as a positive electrode active material capable of sufficiently increasing the charge / discharge capacity in a lithium ion battery without going through the firing step after such a step (X). Can be obtained.

The mixing treatment while applying the compressive force and the shearing force is preferably performed in a closed container equipped with an impeller rotating at a peripheral speed of 30 to 45 m / s. The peripheral speed of the impeller is such that the lithium phosphate compound particles represented by the above formula (I) and the lithium silicate compound particles represented by the above formula (II) are firmly supported, and the resulting lithium ion secondary From the viewpoint of effectively increasing the charge / discharge capacity of the battery, it is preferably 35 to 45 m / s.
The peripheral speed of the impeller means the speed of the outermost end of the rotary stirring blade (impeller), which can be expressed by the following formula (1), and is mixed while applying compressive force and shearing force. The processing time may vary depending on the peripheral speed of the impeller so that it becomes longer as the peripheral speed of the impeller is slower.
Impeller peripheral speed (m / s) =
Impeller radius (m) × 2 × π × rotational speed (rpm) ÷ 60 (1)

  The time for performing the mixing process while applying compressive force and shearing force may vary depending on the peripheral speed of the impeller so that the slower the peripheral speed of the impeller, the more preferably it is 5 to 90 minutes. Preferably it is 10 to 60 minutes. Moreover, the temperature at the time of performing the process which mixes adding a compressive force and a shear force becomes like this. Preferably it is 5-80 degreeC, More preferably, it is 10-50 degreeC. The treatment atmosphere is not particularly limited, but is preferably an inert gas atmosphere or a reducing gas atmosphere.

  Moreover, when carrying | supporting carbon derived from water-insoluble conductive carbon materials other than a cellulose nanofiber on the particle | grain surface of the positive electrode active material composite for lithium ion secondary batteries of this invention, other than a cellulose nanofiber in process (X). A water-insoluble conductive carbon material may be added and mixed with the lithium phosphate compound particles represented by the above formula (I) and the lithium silicate compound particles represented by the above formula (II).

  The peripheral speed and / or treatment time of the impeller in the mixing treatment in the step (X) are the lithium phosphate compound particles represented by the above formula (I) and the silica represented by the above formula (II) that are put into the container. It is necessary to adjust as appropriate according to the amount of the lithium acid compound compound particles or the amount of the water-insoluble conductive carbon material other than the cellulose nanofiber used as necessary. Then, by operating the container, compression force and shearing force are applied to the mixture between the impeller and the inner wall of the container, and the mixture can be mixed. Can be formed into a dense and uniformly dispersed positive electrode active material composite for a lithium ion secondary battery.

For example, when the mixing process is carried out for 10 to 15 minutes in an airtight container equipped with an impeller rotating at a peripheral speed of 35 to 40 m / s, the lithium phosphate compound represented by the above formula (I) to be charged into the container The total amount of the particles, the lithium silicate compound particles represented by the above formula (II), and the water-insoluble conductive carbon material other than the cellulose nanofibers is the effective container (composite Y and the sealed container including the impeller). A container corresponding to a part capable of accommodating carbon black) per cm ³ is preferably 0.1 to 0.7 g, more preferably 0.15 to 0.4 g.

  Examples of the apparatus equipped with a closed container that can easily perform mixing while applying compressive force and shear force include a high-speed shear mill, a blade-type kneader, and the like. Fine particle composite apparatus Nobilta (manufactured by Hosokawa Micron Corporation) can be suitably used.

  When a water-insoluble conductive carbon material other than the cellulose nanofiber is used as the carbon source, the mixture obtained may or may not be baked after step (X). When firing, it is preferably performed in a reducing atmosphere or an inert atmosphere. The firing temperature is preferably 500 to 800 ° C, more preferably 600 to 770 ° C, and further preferably 650 to 750 ° C. The firing time is preferably 10 minutes to 3 hours, more preferably 30 minutes to 1.5 hours.

  As a lithium ion secondary battery to which the positive electrode for a secondary battery including the positive electrode active material composite for a lithium ion secondary battery of the present invention can be applied, a positive electrode, a negative electrode, an electrolytic solution, and a separator are essential components. There is no particular limitation.

  Here, as long as lithium ions can be occluded at the time of charging and released at the time of discharging, the material structure is not particularly limited, and a known material structure can be used. For example, a carbon material such as lithium metal, graphite, or amorphous carbon. It is preferable to use an electrode formed of an intercalating material capable of electrochemically occluding and releasing lithium ions, particularly a carbon material.

  The electrolytic solution is obtained by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent usually used for an electrolyte solution of a lithium ion secondary battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones An oxolane compound or the like can be used.

The type of the supporting salt is not particularly limited, but an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , a derivative of the inorganic salt, LiSO ₃ CF ₃ , LiC (SO ₃ CF ₃ ) ₂ and LiN (SO ₃ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ and LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), organic salts, and derivatives of the organic salts It is preferable that it is at least 1 type of these.

  The separator plays a role of electrically insulating the positive electrode and the negative electrode and holding the electrolytic solution. For example, a porous synthetic resin film, particularly a polyolefin polymer (polyethylene, polypropylene) porous film may be used.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

[Production Example 1: Production of lithium phosphate compound particles (I-1) represented by formula (I)]
1272 g of LiOH.H ₂ O and 4 L of water were mixed to obtain slurry water A. Then, 1153 g of 85% phosphoric acid aqueous solution is dropped at 35 mL / min while stirring the obtained slurry water A at a temperature of 25 ° C. for 2 to 3 minutes, and then stirred at a speed of 400 rpm for 12 hours. to obtain a tricalcium phosphate lithium mixed solution a ¹ by. Such mixture ^{A 1,} compared per mole of phosphorus and contained lithium 2.97 mol. Incidentally, the resulting mixture ^{A 1} is purged with nitrogen, the dissolved oxygen concentration of 0.5 mg / L. Next, 1688 g of MnSO ₄ .5H ₂ O and 834 g of FeSO ₄ .7H ₂ O were added to the total amount of the mixed liquid A ¹ containing the obtained trilithium phosphate to obtain a mixed liquid A ² . At this time, the molar ratio of MnSO ₄ and FeSO ₄ added (manganese compound: iron compound) was 70:30.

Then, a mixed liquid A ² obtained was charged into an autoclave and subjected to 1 hour hydrothermal reaction at 170 ° C.. The pressure in the autoclave was 0.8 MPa. The produced crystal was filtered, and then washed with 12 parts by mass of water with respect to 1 part by mass of the crystal. The washed crystals were lyophilized at −50 ° C. for 12 hours to obtain complex A. The resulting composite A was collected 1000g fraction, to which was added water 1L, to obtain a mixture ^{A 3.} Then, a mixed solution A ³ obtained by dispersion treatment for 1 minute in an ultrasonic agitator (T25, IKA Co.), was evenly colored whole.

The resulting mixture ^{A 4,} after subjecting to spray drying using a spray dryer (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.), under an argon atmosphere of hydrogen (hydrogen concentration: 3%), 1 hour baking at 700 ° C. As a result, lithium phosphate compound particles (I-1) (LiFe _0.3 Mn _0.7 PO ₄ ) represented by the formula (I) were obtained.

[Production Example 2: Production of lithium phosphate compound particles (I-2) represented by formula (I)]
In the production of the mixed solution ^{A 1,} the cellulose nanofibers to the slurry water A (Celish KY-100G, Daicel Finechem manufactured, fiber diameter 4 to 100 nm) except that a mixture of 707g in the same manner as in Production Example 1, 1.2 wt% Lithium phosphate compound particles (I-2) represented by the formula (II) on which carbon derived from cellulose nanofibers is supported (LiFe _0.3 Mn _0.7 PO ₄ / C, amount of carbon = 1.2% by mass) Got.

[Production Example 3: Production of lithium silicate compound particles (II-1) represented by formula (II)]
LiOH · H ₂ O 428g, a mixture of ultra-pure water 3.75L to _{Na 4 SiO 4 · nH 2 O} 1397g to obtain a slurry water C. To this slurry water C, 392 g of FeSO ₄ .7H ₂ O, 793 g of MnSO ₄ .5H ₂ O, and 53 g of Zr (SO ₄ ) ₂ .4H ₂ O were added and mixed to obtain a mixture C ¹ . At this time, the molar ratio of FeSO ₄ , MnSO ₄ and Zr (SO ₄ ) ₂ added (iron compound: manganese compound: zirconium compound) was 28: 66: 3.

Then, the mixture ^{C 1} obtained was charged into an autoclave and subjected to 12hr hydrothermal reaction at 0.99 ° C.. The pressure in the autoclave was 0.4 MPa. The produced crystal was filtered, and then washed with 12 parts by mass of water with respect to 1 part by mass of the crystal. The washed crystals were lyophilized at −50 ° C. for 12 hours to obtain Complex C. The resulting complex C was collected 500g min, to which was added water 5 mL, to give a mixture ^{C 2.} Then, the resulting mixture C ² to dispersion treatment for 1 minute in an ultrasonic agitator (T25, IKA Co.), was evenly colored whole.

The mixture ^{C 3} obtained after subjected to spray drying using a spray dryer (MDL-050M, manufactured by Fujisaki Electric Co., Ltd.), under an argon atmosphere of hydrogen (hydrogen concentration: 3%), 1 hour baking at 650 ° C. As a result, lithium silicate compound particles (II-1) represented by the formula (II) (Li ₂ Fe _0.28 Mn _0.66 Zr _0.03 SiO ₄ ) were obtained.

[Production Example 4: Production of lithium silicate compound particles (II-2) represented by formula (II)]
In the production of the mixed liquid C ¹ , 3.0 mass% in the same manner as in Production Example 1 except that 784 g of cellulose nanofiber (Serish KY-100G, manufactured by Daicel Finechem, fiber diameter 4 to 100 nm) was mixed with the slurry water C. Lithium silicate compound particles (II-2) represented by the formula (I) on which carbon derived from cellulose nanofibers is supported (Li ₂ Fe _0.28 Mn _0.66 Zr _0.03 SiO ₄ / C, amount of carbon = 3. 0% by mass) was obtained.

[Example 1]
A composite of 112 g of lithium phosphate compound particles (I-2) and 48 g of lithium silicate compound particles (II-2) at 40 m / s (6000 rpm) for 30 minutes using Nobilta (manufactured by Hosokawa Micron Corporation, NOB130). The positive electrode active material composite A for lithium ion secondary batteries ((I-2): 70 mass% and (II-2): 30 mass% composite) was obtained.

[Example 2]
Instead of lithium phosphate compound particles (I-2), 112 g of lithium phosphate compound particles (I-1), lithium silicate compound particles (II-) instead of lithium silicate compound particles (II-2) 1) In the same manner as in Example 1, except that 48 g was used and 6.7 g of graphite (UP-5N, manufactured by Nippon Graphite Co., Ltd., equivalent to 4% by mass in terms of carbon atom in the active material) was added. A positive electrode active material composite B for a secondary battery (a composite of (I-1): 67.2 mass%, (II-1): 28.8 mass%, and graphite: 4 mass%) was obtained.

[Example 3]
Positive electrode active material composite C for lithium ion secondary battery in the same manner as in Example 1 except that 48 g of lithium silicate compound particles (II-1) were used instead of lithium silicate compound particles (II-2). ((I-2): 70 mass% and (II-1): 30 mass% complex).

[Example 4]
Instead of lithium silicate compound particles (II-2), 48 g of lithium silicate compound particles (II-1) were used and 6.7 g of graphite (UP-5N, manufactured by Nippon Graphite Co., Ltd., converted into carbon atoms in the active material) The positive electrode active material composite D for lithium ion secondary battery D ((I-2): 67.2 mass%, (II-1) : 28.8 mass%, and graphite: 4 mass%).

[Example 5]
A positive electrode active material for a lithium ion secondary battery in the same manner as in Example 1 except that 6.7 g of graphite (UP-5N, manufactured by Nippon Graphite Co., Ltd., equivalent to 4% by mass in terms of carbon atom in the active material) was added. Composite E ((I-2): 67.2% by mass, (II-2): 28.8% by mass, and graphite: 4% by mass) was obtained.

[Example 6]
144 g of lithium phosphate compound particles (I-2) and 16 g of lithium silicate compound particles (II-2), 6.7 g of graphite (UP-5N, manufactured by Nippon Graphite Co., in terms of carbon atoms in the active material) The positive electrode active material composite F for lithium ion secondary battery F ((I-2): 86.4% by mass, (II-2) : 9.6% by mass, and graphite: 4% by mass).

[Example 7]
128 g of lithium phosphate compound particles (I-2) and 32 g of lithium silicate compound particles (II-2), 6.7 g of graphite (UP-5N, manufactured by Nippon Graphite Co., Ltd., converted into carbon atoms in the active material) The positive electrode active material composite G for lithium ion secondary battery G ((I-2): 76.8% by mass, (II-2) : 19.2 mass% and graphite: 4 mass%).

[Example 8]
96 g of lithium phosphate compound particles (I-2) and 6.7 g of lithium silicate compound particles (II-2), 6.7 g of graphite (UP-5N, manufactured by Nippon Graphite Co., Ltd., carbon in the active material) The positive electrode active material composite H for lithium ion secondary batteries H ((I-2): 57.6 mass%, (II- 2): 38.4% by mass, and graphite: 4% by mass.

[Example 9]
81 g of lithium phosphate compound particles (I-2) and 79 g of lithium silicate compound particles (II-2), 6.7 g of graphite (UP-5N, manufactured by Nippon Graphite Co., in terms of carbon atoms in the active material) The positive electrode active material composite I for lithium ion secondary batteries I ((I-2): 48% by mass, (II-2): 48) Mass% and graphite: 4 mass% composite).

[Comparative Example 1]
Only the lithium phosphate compound particles (I-2) obtained in Production Example 2 were used as the positive electrode active material J for lithium ion secondary batteries ((I-2): 100% by mass).

[Comparative Example 2]
A positive electrode active material mixture K for lithium ion secondary battery K ((I-2): 67.2 mass%, (II-2): 28.8 mass%) in the same manner as in Example 5 except that mixing was performed without using Nobilta. % And graphite: a mixture of 4% by mass).

[Comparative Example 3]
A positive electrode active material mixture L for lithium ion secondary battery L ((I-2): 86.4% by mass, (II-2): 9.6% by mass) in the same manner as in Example 6 except that mixing was performed without using Nobilta. % And graphite: a mixture of 4% by mass).

[Comparative Example 4]
A positive electrode active material mixture M for lithium ion secondary battery M ((I-2): 76.8% by mass, (II-2): 19.2% by mass) in the same manner as in Example 7 except that mixing was performed without using Nobilta. % And graphite: a mixture of 4% by mass).

[Comparative Example 5]
A positive electrode active material mixture N for lithium ion secondary battery N ((I-2): 57.6% by mass, (II-2): 38.4% by mass) in the same manner as in Example 8 except that mixing was performed without using Nobilta. % And graphite: a mixture of 4% by mass).

[Comparative Example 6]
A positive electrode active material mixture O for lithium ion secondary battery O ((I-2): 48% by mass, (II-2): 48% by mass) and graphite in the same manner as in Example 9 except that mixing was performed without using novirta. : 4 mass% mixture).

<< Evaluation of discharge capacity >>
Lithium ion secondary battery positive electrode active material composites A to I or lithium ion secondary battery material particle mixtures J to O obtained in Examples 1 to 9 and Comparative Examples 1 to 6 were used as positive electrode active materials. A positive electrode of an ion secondary battery was produced. Specifically, the positive electrode active material composites A to I for lithium ion secondary batteries or the material particle mixture J to O for lithium ion secondary batteries, ketjen black, and polyvinylidene fluoride in a mass ratio of 75:20: Then, N-methyl-2-pyrrolidone was added thereto and kneaded sufficiently to prepare a positive electrode slurry. The positive electrode slurry was applied to a current collector made of an aluminum foil having a thickness of 20 μm using a coating machine, and vacuum dried at 80 ° C. for 12 hours.
Thereafter, it was punched into a disk shape of φ14 mm and pressed at 16 MPa for 2 minutes using a hand press to obtain a positive electrode.
Next, a coin-type secondary battery was constructed using the positive electrode. A lithium foil (in the case of a lithium ion secondary battery) punched to φ15 mm was used for the negative electrode. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 1 was used. As the separator, a known one such as a polymer porous film such as polypropylene was used. These battery components were assembled and housed in a conventional manner in an atmosphere with a dew point of −50 ° C. or lower to produce a coin-type secondary battery (CR-2032).

A charge / discharge test was performed using the manufactured secondary battery. Specifically, the charging condition is a constant current and constant voltage charging with a current of 0.1 CA (17 mA / g) and a voltage of 4.5 V, the discharging condition is a constant current of 0.1 CA (17 mA / g) and a final voltage of 1.5 V. As the discharge, the discharge capacity at 0.1 CA was determined. Furthermore, 10 cycles were repeatedly tested under the same charge / discharge conditions, and the capacity retention rate (%) was determined by the following formula (1). All charge / discharge tests were performed at 30 ° C.
Capacity retention (%) = (discharge capacity after 10 cycles) / (discharge capacity after 1 cycle)
× 100 (1)
Furthermore, rate characteristics were evaluated using the manufactured secondary battery. Specifically, the charging condition is a constant current and constant voltage charging with a current of 0.1 CA (17 mA / g) and a voltage of 4.5 V, the discharging condition is a constant current of 0.1 CA (170 mA / g) and a final voltage of 1.5 V. As the discharge, the discharge capacity at 1 CA was determined. Furthermore, the ratio of the discharge capacities of 0.1 CA and 1 CA was determined by the following formula (2).
Ratio of discharge capacity (%) = (1 CA discharge capacity per cycle) / (0.1 CA discharge capacity per cycle) × 100 (2)
The results are shown in Table 1.

As is apparent from Table 1, the composite formed by supporting the lithium phosphate compound particles (I) and the lithium silicate compound particles (II) obtained in the examples was used as the positive electrode active material. The lithium ion secondary battery has a high value in all four items of 0.1 CA discharge capacity, capacity retention, 1 CA discharge capacity, and ratio (rate characteristic) of 0.1 CA and 1 CA discharge capacity. In the lithium ion secondary battery using as the positive electrode active material a mixture in which the lithium phosphate compound particles and lithium silicate compound particles obtained in the comparative example were mixed, all of these four items were good. There was nothing that showed a good value.
Thus, the positive electrode active material for a lithium ion secondary battery of the present invention increases the discharge capacity without deteriorating the good capacity retention and rate characteristics that are characteristic of the positive electrode active material comprising a lithium phosphate compound. Can be improved.

Claims (4)

The following formula (I):
LiFe _a Mn _b Mg _c Co _d M ¹ _e PO ₄ (I)
(In formula (I), M ¹ represents Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. A, b, c, d, and e are 0. ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 1, 0 ≦ d ≦ 1, 0 ≦ e ≦ 0.2, and 2 × (a + b + c + d) + ( valence of M ¹ ) × e = 2 And a number satisfying and a + b + c + d ≠ 0.)
Lithium phosphate compound particles represented by the following formula (II):
_{Li 2 Fe f Mn g Co h} Al i M 2 j SiO 4 ··· (II)
(In the formula (II), M ² represents Ni, Zn, V or Zr. F, g, h, i and j are 0 ≦ f ≦ 1, 0 ≦ g ≦ 1, 0 ≦ h ≦ 1, 0. ≦ i ≦ 1, 0 ≦ j <1, and 2 × (f + g + h) + 3 × i + ( valence of M ² ) × j = 2 and a number satisfying f + g + h + i ≠ 0 is shown.
For lithium ion secondary batteries in which the lithium silicate compound particles represented by formula (I) are supported and the content of the lithium phosphate compound particles represented by the formula (I) is 55 to 89% by mass. A method for producing a positive electrode active material composite comprising:
A step of mixing and compounding lithium phosphate compound particles represented by the above formula (I) and lithium silicate compound particles represented by the above formula (II) while applying compressive force and shear force production method for a lithium ion secondary battery Ru with a (X) a positive electrode active material composite. Step a (X), the peripheral speed 30~45m / s in the manufacturing method for a lithium ion secondary battery positive electrode active material composite according to claim 1 carried out in a closed vessel equipped with an impeller rotating. Furthermore, the manufacturing method of the positive electrode active material composite_body | complex for lithium ion secondary batteries of Claim 1 or 2 including the process of adding a cellulose nanofiber or a water-soluble carbon material. The production of the positive electrode active material composite for a lithium ion secondary battery according to any one of claims 1 to 3, further comprising a step of adding a water-insoluble conductive carbon material other than cellulose nanofibers in the step (X). Method.