JP6322729B1 - 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 high cycle characteristics while using a lithium silicate compound, and a method for producing the same I will provide a.
The following formula (I):
Li ₂ Fe _a Mn _b Co _c Al _d M ¹ _e SiO ₄ (I)
Lithium silicate compound particles represented by the following formula (II):
_{LiFe f Mn g Mg h Co i} M 2 j PO 4 ··· (II)
And lithium phosphate compound particles represented by the above formula (II) and the lithium phosphate compound particles represented by the above formula (II). A positive electrode active material composite for a lithium ion secondary battery having a mass ratio ((I) :( II)) to a content of compound particles of 50:50 to 95: 5.
[Selection figure] None

Description

  The present invention relates to a positive electrode active material composite for a lithium ion secondary battery that can effectively improve cycle characteristics 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. Among them, lithium silicate compounds such as Li ₂ FeSiO ₄ having an olivine structure are attracting attention as excellent positive electrode materials used for high-capacity lithium ion secondary batteries, and various developments have been made so far. .

  For example, Patent Document 1 discloses a positive electrode active material containing a solid solution compound that is a lithium silicate compound containing Co and Mn, and a solid-phase reaction through a plurality of firing steps of calcination and main firing of the raw material mixture. A solid solution compound is obtained. Further, Patent Document 2 discloses a silicate compound obtained by mixing a raw material, heating and melting it, and then gradually cooling the melt.

JP 2007-335325 A JP 2008-218303 A

However, in the method described in Patent Document 1, not only a long time is required for production, but the resulting compound tends to increase in particle size by firing at a high temperature. In addition, since the compound obtained by the method described in Patent Document 2 is accompanied by crystallization in the cooling process, it tends to cause variation in composition and crystal type and segregation in the crystal, and when pulverizing a massive cooling product. There is a risk that a large amount of distortion is accumulated in the particles.
Therefore, when these compounds are used as a positive electrode material to obtain a battery, there is a high possibility that the discharge capacity after the second cycle cannot be maintained well even if a high discharge capacity can be shown in the first cycle. In order to realize a useful positive electrode active material using a lithium silicate compound, further improvement is required.

  Accordingly, an object of the present invention is to provide a positive electrode active material composite for a lithium ion secondary battery and a method for producing the same, which can obtain a lithium ion secondary battery having high cycle characteristics while using a lithium silicate compound. It is to provide.

  Therefore, the present inventors have made various studies, and while using a lithium silicate compound mainly, if it is a composite in which lithium silicate compound particles and lithium phosphate compound particles are supported, In the obtained lithium ion secondary battery, it discovered that cycling characteristics could be improved effectively and came to complete this invention.

That is, the present invention provides the following formula (I):
Li ₂ Fe _a Mn _b Co _c Al _d M ¹ _e SiO ₄ (I)
(In the formula (I), M ¹ represents Ni, Zn, V or Zr. A, b, c, d and e are 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 1, 0. ≦ d ≦ 1, 0 ≦ e <1, and 2 × (a + b + c) + 3 × d + (valence of M ¹ ) × e = 2 and a number satisfying a + b + c + d ≠ 0.
Lithium silicate compound particles represented by the following formula (II):
_{LiFe f Mn g Mg h Co i} M 2 j PO 4 ··· (II)
(In formula (II), M ² represents Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. F, g, h, i, and j are 0. ≦ f ≦ 1, 0 ≦ g ≦ 1, 0 ≦ h ≦ 1, 0 ≦ i ≦ 1, 0 ≦ j ≦ 0.2, and 2 × (f + g + h + i) + (valence of M ² ) × j = 2 The number satisfying and f + g + h + i ≠ 0 is shown.)
And lithium phosphate compound particles represented by the above formula (II) and the lithium phosphate compound particles represented by the above formula (II). The present invention provides a positive electrode active material composite for a lithium ion secondary battery having a mass ratio ((I) :( II)) to the content of compound particles of 50:50 to 95: 5.

  The present invention also mixes the lithium silicate compound particles represented by the above formula (I) and the lithium phosphate 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 secondary battery obtained by using the lithium ion secondary battery, a lithium silicate compound is used and discharged every time a charge / discharge cycle is performed. It is possible to effectively suppress a decrease in capacity, and it is possible to maintain excellent cycle characteristics.

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

  The lithium silicate compound particles represented by the above formula (I) and the lithium phosphate compound particles represented by the above formula (II) are both particles having an olivine structure. The former lithium silicate compound particles contain at least one of iron, manganese, cobalt, and aluminum metals, and the latter lithium phosphate compound particles contain at least any transition of iron, manganese, magnesium, and cobalt. 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, Zn, V or Zr, preferably V or Zr, more preferably Zr. a, b, c, and d are 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 1, 0 ≦ d ≦ 1, preferably 0.01 ≦ a ≦ 0.99, 0. 01 ≦ b ≦ 0.99, 0 ≦ c ≦ 0.3, 0 ≦ d ≦ 0.3, more preferably 0.1 ≦ a ≦ 0.9, 0.1 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.15 and 0 ≦ d ≦ 0.15. e is 0 ≦ e <1, and preferably 0 <e <0.2. These a, b, c, d and e are numbers satisfying 2 × (a + b + c) + 3 × d + (valence of M ¹ ) × e = 2 and satisfying a + b + c + d ≠ 0.
Specific examples of the lithium silicate compound particles represented by the formula (I) include, for example, 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. Examples include} Mn _0.45 Zn _0.1 SiO ₄ , Li ₂ Fe _0.36 Mn _0.54 V _0.066 SiO ₄ , Li ₂ Fe _0.282 Mn _0.658 Zr _0.02 SiO ₄ , and among them, Li ₂ Fe _0.282 Mn _0.658 Zr _0.02 SiO ₄ is preferable.

The average particle diameter of the lithium silicate compound particles represented by the above formula (I) 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 (I) is preferably 0.4 to 1.5 g / cm ³ , more preferably 0.5 to 1.4 g / cm ^3. It is.
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, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd, preferably Mg, Zr or Mo. f, g, h, and i are 0 ≦ f ≦ 1, 0 ≦ g ≦ 1, 0 ≦ h ≦ 1, 0 ≦ i ≦ 1, preferably 0.05 ≦ f ≦ 0.95, 0. 01 ≦ g ≦ 1, 0 ≦ h ≦ 0.1, 0 ≦ i ≦ 0.1, more preferably 0.1 ≦ f ≦ 0.9, 0.1 ≦ g ≦ 1, 0 ≦ h ≦ 0 .05, 0 ≦ i ≦ 0.05. j is 0 ≦ j ≦ 0.2, and preferably 0 ≦ j <0.1. F, g, h, i and j are numbers satisfying 2 × (f + g + h + i) + (valence of M ² ) × j = 2 and satisfying f + g + h + i ≠ 0.
Specifically, as the lithium phosphate compound particles represented by the above formula (II), for example, 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 , LiFe _0.19 Mn Examples include _0.75 Zr _0.03 PO ₄ , and LiFe _0.2 Mn _0.8 PO ₄ is particularly preferable.

The average particle diameter of the lithium phosphate compound particles represented by the above formula (II) is preferably 30 to 800 nm, more preferably 40 to 500 nm. The tap density of the lithium phosphate compound particles represented by the formula (II) is preferably 0.4 to 1.5 g / cm, more preferably 0.5 to 1.4 g / cm ³ . is there.

  Mass ratio ((I) :( II)) of the content of lithium silicate compound particles represented by the above formula (I) and the content of lithium phosphate compound particles represented by the above formula (II) Is 50:50 to 95: 5, 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 silicate compound particles represented by the above formula (I) and a plurality of the above formulas (II) while maintaining such a mass ratio. ) -Based lithium phosphate compound particles are particles that are firmly supported while aggregating with each other. By being a composite having such a structure, the lithium silicate compound particles represented by the above formula (I) and the lithium phosphate compound particles represented by the above formula (II) act synergistically. In other words, when a lithium ion secondary battery is constructed, it is possible to express cycle characteristics superior to the case where a positive electrode active material composed only of a lithium silicate compound is used. This is because the lithium silicate compound particles represented by the above formula (I) have a large volume change during charge and discharge, while the lithium phosphate compound particles represented by the above formula (II) are represented by the above formula (I). Since the volume change is small compared to the lithium silicate compound particles represented, it is estimated that the volume change during charging / discharging can be comprehensively suppressed by supporting these particles to form a composite. .

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

  The particle surface of the lithium silicate compound represented by the above formula (I), or the lithium silicate compound particles represented by the above formula (I), and the lithium phosphate compound represented by the above formula (II) It is preferable that carbon derived from cellulose nanofibers or carbon derived from a water-soluble carbon material is supported on both particle surfaces of the particles. By supporting such carbon, when the positive electrode active material composite for a lithium ion secondary battery obtained from this is used as a positive electrode for a lithium ion secondary battery, the activity associated with the volume change of the active material particles during charge / discharge It is presumed that the deterioration of the conductive path between the substance particles can be suppressed and excellent cycle characteristics can be expressed.

  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 cycle characteristics 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 silicate compound particles represented by the formula (I) or the surface of the lithium phosphate 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 a lithium silicate compound particle represented by the above formula (I) or a lithium phosphate 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 silicate compound particles represented by the above formula (I) or the lithium phosphate compound particles represented by the above formula (II) are prepared by adding a silicate compound or a phosphate compound to the 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 cobalt compound, or an aluminum compound, or a metal salt containing at least one of an iron compound, a manganese compound, a magnesium compound, or a cobalt compound (B) to obtain a composite B by subjecting the slurry water B containing a hydrothermal reaction to the slurry water B, and a step (C) to fire the obtained composite B
The lithium silicate compound particles represented by the above formula (I) and the lithium phosphate compound particles represented by the above formula (II) are independent of each other. To obtain as separate and independent particles.
That is, when obtaining the lithium silicate compound particles represented by the above formula (I), a silicate compound is used in the step (A), and at least an iron compound, a manganese compound, a cobalt compound, or a step (B). What is necessary is just to use the metal salt containing either of an aluminum compound, and when obtaining the lithium phosphate type compound particle | grains represented by the said Formula (II), a phosphoric acid compound is used in a process (A), and a process (B) In this case, a metal salt containing at least one of an iron compound, a manganese compound, a magnesium compound, or a cobalt compound may be used. In the case where carbon derived from cellulose nanofibers or water-soluble carbon material is supported on the surface of these lithium compound particles, cellulose nanofibers or water-soluble carbon materials are used in step (A) or step (B). May be added.

The step (A) is a step of obtaining the composite A by mixing the silicate compound or the phosphate 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 silicate compound is used in the step (A), the content of the silicate compound in the mixture A is preferably 5 to 40 parts by mass, more preferably 100 parts by mass of water. 7 to 35 parts by mass. Moreover, when a phosphoric acid compound is used, the content of the lithium compound in the mixture A is preferably 5 to 50 parts by mass, more preferably 10 to 45 parts by mass with respect to 100 parts by mass of water.

  Prior to mixing the silicic acid compound or the phosphoric acid compound with the mixture A, the mixture A is preferably stirred 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.

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. .

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

  Lithium silicate compound particles represented by the above formula (I) are obtained by purging nitrogen with respect to the mixture A after mixing the silicate compound or phosphate compound to complete the reaction in the mixture. Alternatively, complex A, which is a precursor of lithium phosphate compound particles represented by the above formula (II), is generated 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 silicate compound particles represented by the above formula (I) or the precursor of the lithium phosphate 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 silicic acid compound or a phosphoric 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 silicic acid compound or a phosphoric 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 reducing the size of the dispersed particles, the dissolved oxygen concentration in the mixture A after mixing the silicic acid compound or the phosphoric acid compound is reduced 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 a metal salt containing at least one of an iron compound, a manganese compound, or an aluminum compound, or at least an iron compound, a manganese compound, a magnesium compound, or cobalt In this step, the slurry B containing a metal salt containing any one of the compounds is subjected to a hydrothermal reaction to obtain the composite B. The complex A obtained by the step (A) is a mixture of the lithium silicate compound particles represented by the formula (I) or the lithium phosphate compound particles represented by the formula (II). As a precursor, 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 (I). Then, 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 (II), and slurry water is added. It is preferable to use as B. As a result, the lithium silicate compound particles represented by the above formula (I) or the lithium phosphate compound particles represented by the above formula (II) become extremely 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, excellent cycle characteristics 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 silicic acid or phosphoric acid in the mixture obtained in A).

  The amount of water used for the hydrothermal reaction is the silicic acid or phosphate ion 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 50 mol, more preferably 12 when the ions contained in the slurry water B are silicate ions. .5 to 45 moles. Moreover, when the ion contained in the slurry water B is a phosphate ion, Preferably it is 10-30 mol, More preferably, it is 12.5-25 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 silicate compound particles represented by the above formula (I) or lithium phosphate 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 silicate compound particles represented by the above formula (I) or the lithium phosphate 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 silicate compound particle represented by the above formula (I) and a lithium phosphate 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. Furthermore, the BET specific surface area of the positive electrode active material composite for a lithium ion secondary battery of the present invention is preferably 5 to 40 m ² / g, more preferably 7 to 30 m ² / g, from the viewpoint of improving cycle characteristics. It is.

  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 silicate compound represented by the above formula (I) formed by supporting the carbon, not only the particle surface of the positive electrode active material composite for a lithium ion secondary battery but also aggregating and supporting each other. Carbon can also be interspersed or interspersed between the particles and the lithium phosphate compound particles represented by the above formula (II), and when this is used as a positive electrode for a lithium ion secondary battery, the battery performance is further improved. This can contribute to the improvement of cycle characteristics.

  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 improving cycle characteristics. . 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 silicate compound particles represented by the above formula (I) (supporting carbon derived from cellulose nanofibers and water-soluble carbon material) and phosphoric 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 silicate compound particles represented by the above formula (I) (without supporting carbon derived from cellulose nanofibers and water-soluble carbon material) and phosphoric 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 silicate-based compound particles represented by the above formula (I) (supporting carbon derived from cellulose nanofibers and water-soluble carbon material) and phosphoric 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 silicate compound particles represented by the above formula (I) (supporting carbon derived from cellulose nanofibers and water-soluble carbon material) and phosphoric 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 silicate compound particles represented by the above formula (I) (supporting carbon derived from cellulose nanofibers and water-soluble carbon material) and phosphoric 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 silicate compound particle represented by the above formula (I) and a lithium phosphate 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 silicate compound particles represented by the above formula (I) and the lithium phosphate compound particles represented by the above formula (II), the compression force and The step of mixing while applying a shearing force is preferred. Thus, the lithium silicate compound particles represented by the above formula (I) and the lithium phosphate compound particles represented by the above formula (II) can be supported while firmly agglomerated while being uniformly dispersed. A positive electrode active material composite for a lithium ion secondary battery, which is useful as a positive electrode active material capable of improving cycle characteristics in a lithium ion secondary battery without going through a 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 lithium silicate compound particles represented by the above formula (I) and lithium phosphate compound particles represented by the above formula (II) are firmly supported, and the resulting lithium ion secondary From the viewpoint of effectively improving the cycle characteristics 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 silicate compound particles represented by the above formula (I) and the lithium phosphate 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) is the lithium silicate compound particles represented by the above formula (I) and phosphorus represented by the above formula (II) to be 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, in the case where the mixing process is performed 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 silicate compound represented by the above formula (I) is charged into the container The total amount of the particles, the lithium phosphate compound particles represented by the above formula (II), and the water-insoluble conductive carbon material other than the cellulose nanofiber is the effective container (composite Y and 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 silicate compound particles (I-1) represented by formula (I)]
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 (I-1) represented by the formula (I) (Li ₂ Fe _0.28 Mn _0.66 Zr _0.03 SiO ₄ ) were obtained.

[Production Example 2: Production of lithium silicate compound particles (I-2) represented by formula (I)]
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 (I-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.

[Production Example 3: Production of lithium phosphate compound particles (II-1) represented by formula (II)]
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 (II-1) (LiFe _0.3 Mn _0.7 PO ₄ ) represented by the formula (II) were obtained.

[Production Example 4: Production of lithium phosphate compound particles (II-2) represented by formula (II)]
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 3, 1.2 wt% Lithium phosphate compound particles (II-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.

[Example 1]
Compound of 112 g of lithium silicate compound particles (I-2) and 48 g of lithium phosphate compound particles (II-2) at 40 m / s (6000 rpm) for 30 minutes using Nobilta (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]
112 g lithium silicate compound particles (I-1) instead of lithium silicate compound particles (I-2), lithium phosphate compound particles (II-) instead of lithium phosphate 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 phosphate compound particles (II-1) were used instead of lithium phosphate compound particles (II-2). ((I-2): 70 mass% and (II-1): 30 mass% complex).

[Example 4]
Instead of lithium phosphate compound particles (II-2), 48 g of lithium phosphate 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]
Lithium silicate compound particles (I-2) 144g, lithium phosphate compound particles (II-2) 16g, graphite 6.7g (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 silicate compound particles (I-2) and 32 g of lithium phosphate 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 silicate compound particles (I-2) and 6.7 g of lithium phosphate 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]
80 g of lithium silicate compound particles (I-2) and 80 g of lithium phosphate compound particles (II-2), 6.7 g of graphite (UP-5N, Nippon Graphite Co., Ltd., converted into 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 silicate 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): 70% by mass and (II-2): 30% by mass) in the same manner as in Example 1 except that the mixture was used without using Nobilta. )

[Comparative Example 3]
A positive electrode active material mixture L for lithium ion secondary battery L ((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 4]
A positive electrode active material mixture M for lithium ion secondary battery M ((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 5]
A positive electrode active material mixture N for lithium ion secondary battery N ((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 6]
A positive electrode active material mixture O for lithium ion secondary battery O ((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 7]
A positive electrode active material mixture P for lithium ion secondary battery P ((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 Nobilta. : 4 mass% mixture).

<Evaluation of capacity retention>
Using the positive electrode active material composites A to I for lithium ion secondary batteries or the material particle mixtures J to P for lithium ion secondary batteries obtained in Examples 1 to 9 and Comparative Examples 1 to 7, lithium ion secondary batteries A positive electrode was prepared. Specifically, the positive electrode active material composites A to I for lithium ion secondary batteries or the material particle mixtures J to P 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 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)
The results are shown in Table 1.

  As is apparent from Table 1, the composite formed by supporting the lithium silicate compound particles (I) and the lithium phosphate compound particles (II) obtained in the examples was used as the positive electrode active material. Lithium ion secondary battery, compared with lithium ion secondary battery using as a positive electrode active material a mixture of lithium silicate compound particles and lithium phosphate compound particles obtained in Comparative Example, It can be seen that it has a high capacity retention rate and excellent cycle characteristics.

Claims (4)

The following formula (I):
Li ₂ Fe _a Mn _b Co _c Al _d M ¹ _e SiO ₄ (I)
(In the formula (I), M ¹ represents Ni, Zn, V or Zr. A, b, c, d and e are 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 1, 0. ≦ d ≦ 1, 0 ≦ e <1, and 2 × (a + b + c) + 3 × d + ( valence of M ¹ ) × e = 2 and a number satisfying a + b + c + d ≠ 0.
Lithium silicate compound particles represented by the following formula (II):
_{LiFe f Mn g Mg h Co i} M 2 j PO 4 ··· (II)
(In formula (II), M ² represents Ni, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. F, g, h, i, and j are 0. ≦ f ≦ 1, 0 ≦ g ≦ 1, 0 ≦ h ≦ 1, 0 ≦ i ≦ 1, 0 ≦ j ≦ 0.2, and 2 × (f + g + h + i) + ( valence of M ² ) × j = 2 The number satisfying and f + g + h + i ≠ 0 is shown.)
And the lithium phosphate compound compound represented by the above formula (II) and the lithium phosphate compound compound represented by the above formula (II). The mass ratio ((I) :( II)) to the content of particles is a method for producing a positive electrode active material composite for a lithium ion secondary battery having a mass ratio of 50:50 to 95: 5,
A step of mixing and compounding the lithium silicate compound particles represented by the above formula (I) and the lithium phosphate 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.