JP6264407B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery.

In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been proposed and put into practical use as batteries that are expected to be reduced in size, weight, and capacity. A lithium ion secondary battery is composed of a positive electrode and a negative electrode having a property capable of reversibly removing and inserting lithium ions, and a non-aqueous electrolyte.
Generally as a negative electrode active material of the negative electrode material of a lithium ion secondary battery, the carbon-type material or the Li containing metal oxide which has a property which can reversibly insert and remove lithium ion is used. Examples of such a Li-containing metal oxide include lithium titanate (Li ₄ Ti ₅ O ₁₂ ).

On the other hand, as a positive electrode material of a lithium ion secondary battery, a positive electrode material mixture including a positive electrode active material and a binder is used. As the positive electrode active material, for example, a Li-containing metal oxide having a property capable of reversibly removing and inserting lithium ions such as lithium iron phosphate (LiFePO ₄ ) is used. And the positive electrode of a lithium ion secondary battery is formed by apply | coating this positive electrode material mixture on the surface of metal foil called a collector.

  A non-aqueous solvent is used for the electrolyte of the lithium ion secondary battery. As the non-aqueous solvent, a positive electrode active material that is oxidized / reduced at a high potential and a negative electrode active material that is oxidized / reduced at a low potential can be applied, and a lithium ion secondary battery having a higher voltage can be realized.

  Such a lithium ion secondary battery is lighter and smaller than conventional secondary batteries such as a lead battery, a nickel cadmium battery, and a nickel metal hydride battery, and has high energy. Therefore, lithium ion secondary batteries are used not only as small power sources used for portable electronic devices such as portable telephones and notebook personal computers, but also as stationary emergency large power sources.

  In order to obtain a positive electrode active material capable of realizing a nonaqueous electrolyte secondary battery excellent in all of cycle characteristics, storage characteristics and continuous charge characteristics, the positive electrode active material includes a lithium transition metal oxide and an oxo acid salt. , A group detected by TEM-EDX analysis of the cross section of the positive electrode active material, TOF-SIMS in the depth direction of the positive electrode active material, or XPS in the depth direction of the positive electrode active material, at least consisting of phosphorus, sulfur and boron A peak derived from at least one element selected from (A), and a peak derived from at least one element selected from the group consisting of transition metals (B), at least one peak (A), and at least It is disclosed that one peak (B) satisfies a predetermined relationship (for example, see Patent Document 1).

Japanese Patent Laying-Open No. 2015-099659

However, even if the electrode material for a secondary battery disclosed in Patent Document 1 is used, the deterioration of the long-term cycle characteristics cannot be controlled.
This invention is made | formed in view of the said situation, Comprising: It aims at providing the lithium ion secondary battery which is excellent in long-term cycling characteristics.

As a result of intensive studies, the present inventors applied a positive electrode including positive electrode active material particles made of lithium phosphate having an oxidation-reduction potential below 4.2 V (Li / Li +) to a lithium ion secondary battery. It has been found that when the lithium ion secondary battery contains inorganic phosphate particles, a lithium ion secondary battery having excellent long-term cycle characteristics can be obtained.
Although the detailed mechanism for improving the long-term cycle characteristics of the battery is not clear because the battery contains inorganic phosphate particles, the inorganic phosphate particles react with the transition metal ions eluted from the positive electrode, and transition metal ions This is thought to be because it is possible to suppress the dissolution of transition metal from the positive electrode material.

In addition, as a result of intensive studies, the present inventors have found that a lithium ion secondary battery including a positive electrode and a negative electrode made of natural graphite has a battery voltage of 4.1 V at a current value of 2 C in a 60 ° C. environment. After charging at constant current until the battery voltage reaches 2V at a current value of 2C,
During the one cycle, the charge capacity at the time of constant current charging until the battery voltage becomes 4.1V at a current value of 2C is defined as a charge capacity A, and then discharged until the battery voltage becomes 2V at a current value of 2C. When the discharge capacity at the time is defined as discharge capacity B, the integrated value when the difference between the discharge capacity B and the charge capacity A in one cycle (discharge capacity B−charge capacity A) is integrated over 500 cycles is 100 mAh / g. It was found that the lithium ion secondary battery in which the discharge capacity B in the first cycle is 100 mAh / g or more is excellent in long-term cycle characteristics. From the above ideas, the present invention has been completed.
That is, the present invention provides the following means.

The lithium ion secondary battery of the present invention is a lithium ion secondary battery including a positive electrode, a negative electrode, and an electrolyte, and contains inorganic phosphate particles. The positive electrode is LixAyMzPO ₄ (0 ≦ x ≦ 1.1, 0.8 ≦ y ≦ 1.1, 0 ≦ z ≦ 0.2, where A is at least one selected from the group consisting of Fe, Mn, Co, and Ni, and M is Mg , Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and at least one selected from the group consisting of rare earth elements), and the surface of the center particle is coated Containing positive electrode active material particles having a carbonaceous coating film.

  According to the present invention, a lithium ion secondary battery excellent in long-term cycle characteristics can be obtained.

It is a figure which shows the integration irreversible capacity | capacitance value fluctuation | variation at the time of the cycle test in Example 1 and Comparative Example 1. FIG.

Embodiments of the lithium ion secondary battery of the present invention will be described.
Note that this embodiment is specifically described in order to better understand the gist of the invention, and does not limit the present invention unless otherwise specified.

<Lithium ion secondary battery>
The lithium ion secondary battery of the present embodiment is a lithium ion secondary battery including a positive electrode, a negative electrode, and an electrolyte,
Contains inorganic phosphate particles,
The positive electrode is LixAyMzPO ₄ (0 ≦ x ≦ 1.1, 0.8 ≦ y ≦ 1.1, 0 ≦ z ≦ 0.2, where A is selected from the group consisting of Fe, Mn, Co, and Ni M is at least one selected from the group consisting of Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and rare earth elements) And positive electrode active material particles having a carbonaceous film covering the surface of the center particle.
The inorganic phosphate particles may be included in the positive electrode, may be included in the negative electrode, may be included in the electrolyte, or other components that the lithium ion secondary battery may have. It may be included. Details of the content of the inorganic phosphate particles will be described later.
Although details of the positive electrode, the negative electrode, and the electrolyte included in the lithium ion secondary battery of the present embodiment will be described later, the following configuration can be adopted.
The positive electrode of the present embodiment can include, for example, a current collector made of a metal foil and a positive electrode mixture layer formed on the current collector. The negative electrode of this embodiment can be comprised including various negative electrode materials. The positive electrode of this embodiment and the negative electrode of this embodiment can be made to oppose via a separator. As the electrolyte of the present embodiment, a non-aqueous electrolyte can be used, and a liquid electrolyte is usually used.

[Inorganic phosphate particles]
The inorganic phosphate particles are not particularly limited as long as they are particles containing inorganic phosphate, but preferably contain at least one selected from the group consisting of alkali metals and alkaline earth metals. It is preferable that the inorganic phosphate particles further contain at least one selected from the group consisting of phosphoric acid, pyrophosphoric acid, and metaphosphoric acid.
The inorganic phosphate particles may be crystalline or amorphous.

The inorganic phosphate particles may contain a base metal, a metalloid or a transition metal, but the content in the inorganic phosphate particles is such that the transition metal / phosphorus ratio is 0.5 (molar ratio) in terms of the substance amount ratio (molar ratio). The range is preferably within the following range, and more preferably 0.1 or less. The transition metal may not be contained in the inorganic phosphate particles.
When the transition metal / phosphorus ratio is 0.5 or less in molar ratio, desorption of alkali metal and alkaline earth metal due to oxidation / reduction of transition metal hardly occurs, structural change of inorganic phosphate particles and expansion / contraction of volume Therefore, it is difficult to cause destruction of the mixture electrode structure.

The inorganic phosphate particles may be represented by Li _α P _β O _γ (0 <α ≦ 3, 0 <β ≦ 2, 0 <γ ≦ 4, 0.5 ≦ α / β ≦ 3.5). Preferably, 0.9 ≦ α / β ≦ 2.1. By setting the inorganic phosphate particles to Li _α P _β O _γ (0 <α ≦ 3, 0 <β ≦ 2, 0 <γ ≦ 4, 0.5 ≦ α / β ≦ 3.5), It is possible to efficiently suppress elution of the transition metal.

The average primary particle diameter of the primary particles of the inorganic phosphate particles is preferably 0.5 μm or more and 75 μm or less, and more preferably 0.5 μm or more and 45 μm or less.
If the average primary particle diameter of the primary particles of the inorganic phosphate particles is 0.5 μm or more, it is difficult to take a form in which the inorganic phosphate particles are coated on the surface of the positive electrode active material particles. Transition metal elution can be suppressed.
On the other hand, when the average primary particle diameter of the primary particles of the inorganic phosphate particles is 75 μm or less, it is difficult to form irregularities on the electrode, so that a uniform electrode can be produced and current density unevenness can be suppressed. it can.

[Method for producing inorganic phosphate particles]
As a method for producing inorganic phosphate particles in the present embodiment, a conventional method such as a solid phase method, a liquid phase method, or a gas phase method can be used.

  The manufacturing method of inorganic phosphate particles in the present embodiment includes, for example, a mixing step of inorganic phosphate particle raw materials, a baking step of baking the obtained inorganic phosphate particles, and the obtained inorganic phosphate particles. And a classification step of classifying the pulverized inorganic phosphate particles.

(Inorganic phosphate raw material mixing process)
As a method for mixing the raw material of the inorganic phosphate particles, the raw material may be mixed in a solid phase, mixed in a liquid phase, or mixed in a gas phase. Is preferred. When the raw materials are pulverized and mixed using a pulverizer or the like, it can be mixed more uniformly, which is more preferable.

  The raw material of the inorganic phosphate particles includes at least one of a phosphoric acid source, an alkali metal source, and an alkaline earth metal source, and may further include a base metal source, a semimetal source, and a transition metal source.

Here, phosphoric acid sources include phosphoric acid (H ₃ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), pyrophosphoric acid ( Phosphoric acid compounds such as H ₄ P ₂ O ₇ ), alkali metal or alkaline earth metal phosphates, and the like are preferably used.

  As the alkali metal source, phosphates, acetates, sulfates, hydrochlorides, nitrates, hydroxides, citrates and the like containing Li, Na, K, Rb and the like are preferably used.

  As the alkaline earth metal source, phosphates, acetates, sulfates, hydrochlorides, nitrates, hydroxides, citrates and the like containing Be, Mg, Ca, Sr, Ba and the like are preferably used.

  As the base metal source, phosphates, acetates, sulfates, hydrochlorides, nitrates, hydroxides, citrates and the like containing Al, Ga, In, Sn, Pb and the like are preferably used.

  As the metalloid source, phosphates, acetates, sulfates, hydrochlorides, nitrates, hydroxides, citrates and the like containing B, Si, Ge, As, Sb, Te and the like are preferably used.

  Examples of transition metal sources include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Ta, W, etc. Phosphate, acetate, sulfate, hydrochloride, nitrate, hydroxide, citrate and the like containing

(Baking process)
Next, the obtained mixture is fired at a temperature of preferably 300 ° C. or higher and 1000 ° C. or lower, more preferably 500 ° C. or higher and 800 ° C. or lower for 0.1 hour or longer and 40 hours or shorter.
Here, by setting the firing temperature to 300 ° C. or higher, the inorganic phosphate raw material can be sufficiently reacted, and inorganic phosphate particles with few impurities can be produced. On the other hand, by setting the firing temperature to 1000 ° C. or less, the inorganic phosphate particles can be prevented from growing beyond the target size, for example, the evaporation of lithium (Li), which is an alkali metal, can be suppressed. Since it can be suppressed when it is desired to suppress amorphization, inorganic phosphate particles having good characteristics can be obtained.

The firing atmosphere may be an oxidizing atmosphere or a non-oxidizing atmosphere. The oxidizing atmosphere may be in the air, or may be an atmosphere in which oxygen (O ₂ ) is introduced to increase the oxygen concentration. As the non-oxidizing atmosphere, an atmosphere made of an inert gas such as nitrogen (N ₂ ) or argon (Ar) is preferable.

(Crushing process)
Next, when it is desired to adjust the particle diameter of the obtained inorganic phosphate, pulverization may be performed. The pulverization method may be either a wet method or a dry method. When pulverizing, it is preferable that the pulverizing strength is such that inorganic phosphate particles having a primary particle diameter of 75 μm or more are eliminated. This is because when the primary particle diameter of the inorganic phosphate particles is 75 μm or less, it is difficult to form irregularities on the electrode, so that a uniform electrode can be produced and uneven current density can be suppressed.

(Classification process)
Next, the inorganic phosphate particles are classified. Classification may be either a wet method or a dry method. Moreover, the classification using airflow may be sufficient and the classification using a sieve may be sufficient. In this case, it is preferable to classify the inorganic phosphate particles so that the particle diameter thereof is 75 μm or less. This is because when the primary particle diameter of the inorganic phosphate particles is 75 μm or less, it is difficult to form irregularities on the electrode, so that a uniform electrode can be produced and uneven current density can be suppressed.

[Contained form of inorganic phosphate particles]
The inorganic phosphate particles may be contained in the positive electrode mixture layer, may be present between the positive electrode mixture layer and the separator, or may be supported on the separator. In addition, it may be contained in the electrolyte, may be contained in the negative electrode mixture layer, and may be contained in one or more places. Among these, the form contained in the positive electrode mixture layer (contained in the positive electrode) is preferable.
Since the inorganic phosphate particles of the present embodiment play a role of suppressing elution of transition metals from the positive electrode, a lithium ion secondary battery excellent in long-term cycle stability and safety can be realized.

When the inorganic phosphate particles are included in the positive electrode mixture layer, the positive electrode mixture layer is preferably composed of composite particles in which the positive electrode active material particles are attached to the surface of the inorganic phosphate particles.
Elution of transition metal from the positive electrode by forming the composite particles in a form in which the positive electrode active material particles are attached to the surface of the inorganic phosphate particles without forming the positive electrode active material particles on the surface of the inorganic phosphate. It is easy to suppress.

  The optimum mixing ratio of the positive electrode active material particles and the inorganic phosphate particles is determined according to the primary particle diameter of the positive electrode active material particles, the primary particle diameter of the inorganic phosphate particles, and the like. It is preferable that the inorganic phosphate particles are contained in an amount of 0.1 parts by mass or more and 10 parts by mass or less, more preferably 0.2 parts by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the active material particles. , 0.5 parts by mass or more and 7 parts by mass or less are further preferable, and 0.5 part by mass or more and 6 parts by mass or less are further more preferable. Elution of the transition metal from a positive electrode can fully be suppressed as an inorganic phosphate particle is 0.1 mass part or more with respect to 100 mass parts of positive electrode active material particles. On the other hand, when the inorganic phosphate particles are 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material particles, the inorganic phosphate particles having low electron conductivity do not impair the electron conduction of the positive electrode mixture layer, It can suppress that the capacity | capacitance of a lithium ion secondary battery falls.

  When the inorganic phosphate particles are included between the positive electrode mixture layer and the separator, it is preferable that the inorganic phosphate particles are uniformly present in the inorganic phosphate particle layer between the positive electrode mixture layer and the separator. . By uniformly presenting the inorganic phosphate particles, unevenness can be reduced, current density bias can be prevented, and transition metals eluted from the positive electrode can be efficiently captured.

  The thickness of the inorganic phosphate particle layer is preferably 0.5 μm or more and 35 μm or less. If the thickness of the inorganic phosphate layer is 0.5 μm or more, the transition metal eluted from the positive electrode can be efficiently captured, and if it is 35 μm or less, the liquid resistance derived from ion migration between the positive electrode and the negative electrode can be reduced. Can do.

  When the inorganic phosphate particles are included in the electrolyte, it is preferable that the inorganic phosphate particles are uniformly dispersed in the electrolyte. By uniformly dispersing the inorganic phosphate particles, unevenness can be reduced, current density can be prevented from being uneven, and transition metals eluted from the positive electrode can be efficiently captured.

  When the inorganic phosphate particles are supported on the separator, it is preferable that the inorganic phosphate particles are uniformly dispersed in the electrolyte. By uniformly dispersing the inorganic phosphate particles, unevenness can be reduced, current density can be prevented from being uneven, and transition metals eluted from the positive electrode can be efficiently captured.

[Positive electrode]
The positive electrode of this embodiment is LixAyMzPO ₄ (0 ≦ x ≦ 1.1, 0.8 ≦ y ≦ 1.1, 0 ≦ z ≦ 0.2, where A is made of Fe, Mn, Co, and Ni. And at least one selected from the group consisting of Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and rare earth elements. And positive electrode active material particles having a carbonaceous film covering the surface of the center particles.
The positive electrode of the present embodiment includes a current collector made of metal foil and a positive electrode mixture layer formed on the current collector, and the positive electrode mixture layer contains the positive electrode active material particles of the present embodiment. It is preferable to do. The positive electrode of the present embodiment is preferably formed by using the positive electrode material containing the positive electrode active material particles of the present embodiment and forming a positive electrode mixture layer on one main surface of the current collector.

(Positive electrode active material particles)
The positive electrode active material particles are LixAyMzPO ₄ (0 ≦ x ≦ 1.1, 0.8 ≦ y ≦ 1.1, 0 ≦ z ≦ 0.2, where A is a group consisting of Fe, Mn, Co, and Ni. And at least one selected from the group consisting of Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and rare earth elements. And a carbonaceous film covering the surface of the central particle.

The average primary particle diameter of the positive electrode active material particles is preferably 10 nm or more and 700 nm or less, and more preferably 20 nm or more and 500 nm or less.
When the average primary particle diameter of the positive electrode active material particles is 10 nm or more, an increase in the carbon mass required by increasing the specific surface area of the positive electrode active material particles is suppressed, and the charge / discharge capacity of the lithium ion secondary battery is reduced. Can be suppressed. On the other hand, when the average primary particle diameter of the positive electrode active material particles is 700 nm or less, it is possible to suppress an increase in the time required for movement of lithium ions or electrons within the positive electrode active material particles. Thereby, it can suppress that the internal resistance of a lithium ion secondary battery increases and an output characteristic deteriorates.

  Here, the average particle diameter is a volume average particle diameter. The average primary particle diameter of the primary particles of the central particles can be measured using a laser diffraction / scattering particle size distribution measuring device or the like. Alternatively, a plurality of primary particles observed with a scanning electron microscope (SEM) may be arbitrarily selected, and the average particle diameter of the primary particles may be calculated.

[Center particle]
The central particles constituting the positive electrode active material particles in this embodiment are LixAyMzPO ₄ (0 ≦ x ≦ 1.1, 0.8 ≦ y ≦ 1.1, 0 ≦ z ≦ 0.2, where A is Fe, At least one selected from the group consisting of Mn, Co, and Ni, and M is Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and rare earth elements. At least one selected from the group consisting of:
The rare earth elements are 15 elements of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, which are lanthanum series.

The average primary particle size of the primary particles of the central particles constituting the positive electrode active material particles in the present embodiment is preferably 5 nm or more and 800 m or less, and more preferably 20 nm or more and 500 nm or less.
When the average primary particle diameter of the primary particles of the central particles is 5 nm or more, the surface of the primary particles of the central particles can be sufficiently covered with the carbonaceous film. And the discharge capacity in the high-speed charging / discharging of a lithium ion secondary battery can be made high, and sufficient charging / discharging performance can be implement | achieved. On the other hand, when the average primary particle diameter of the primary particles of the central particles is 500 nm or less, the internal resistance of the primary particles of the central particles can be reduced. And the discharge capacity in the high-speed charge / discharge of a lithium ion secondary battery can be made high.

The shape of the primary particles of the central particles constituting the positive electrode active material particles in the present embodiment is not particularly limited, but it is easy to generate a positive electrode active material composed of spherical, particularly spherical, secondary particles. The shape of is preferably spherical.
The amount of the solvent when preparing the positive electrode material paste by mixing the positive electrode material containing the positive electrode active material particles, the binder resin (binder), and the solvent because the shape of the primary particles of the central particles is spherical. Can be reduced. In addition, since the shape of the primary particles of the central particles is spherical, it becomes easy to apply the positive electrode material paste to the current collector. Further, if the shape of the primary particles of the central particles is spherical, the surface area of the primary particles of the central particles is minimized, and the amount of binder resin (binder) in the positive electrode material paste can be minimized. As a result, the internal resistance of the positive electrode of this embodiment can be reduced. Further, if the shape of the primary particles of the center particle is spherical, the positive electrode active material particles are easily packed most closely, so that the amount of the positive electrode active material particles per unit volume of the positive electrode increases. As a result, the positive electrode density can be increased, and a high-capacity lithium ion secondary battery can be obtained.

[Carbonaceous film]
The carbonaceous coating covers the surface of the central particle.
By covering the surface of the center particle with the carbonaceous film, the electrical conductivity of the positive electrode active material particles can be improved.
The thickness of the carbonaceous film is preferably 0.2 nm or more and 10 nm or less, and more preferably 0.5 nm or more and 4 nm or less.
When the thickness of the carbonaceous film is 0.2 nm or more, it can be suppressed that a film having a desired resistance value cannot be formed because the thickness of the carbonaceous film is too thin. And the electroconductivity as a positive electrode active material particle is securable. On the other hand, it can suppress that the battery capacity per unit mass of a positive electrode active material particle falls that the thickness of a carbonaceous film is 10 nm or less.
Further, when the thickness of the carbonaceous film is 0.2 nm or more and 10 nm or less, the positive electrode active material particles are easily packed most closely, so that the amount of the positive electrode active material particles per unit volume of the positive electrode increases. As a result, the positive electrode density can be increased, and a high-capacity lithium ion secondary battery can be obtained.

The amount of carbon contained in the positive electrode active material particles is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.3% by mass or more and 3% by mass or less.
When the carbon content is 0.1% by mass or more, the discharge capacity at the high-speed charge / discharge rate of the lithium ion secondary battery is increased, and sufficient charge / discharge rate performance can be realized. On the other hand, it can suppress that the battery capacity of the lithium ion secondary battery per unit mass of positive electrode active material particles falls more than necessary that carbon content is 10 mass% or less.

The amount of carbon supported relative to the specific surface area of the primary particles of the central particles constituting the positive electrode active material particles (“[carbon supported amount] / [specific surface area of the primary particles of the central particles]”; hereinafter referred to as “carbon supported amount ratio”) is 0.01 or more and 0.5 or less, more preferably 0.03 or more and 0.3 or less.
When the carbon loading ratio is 0.01 or more, the discharge capacity at a high-speed charge / discharge rate of the lithium ion secondary battery is increased, and sufficient charge / discharge rate performance can be realized. On the other hand, it can suppress that the battery capacity of the lithium ion secondary battery per unit mass of positive electrode active material particle falls more than necessary as the carbon carrying amount ratio is 0.5 or less.

The specific surface area of the positive electrode active material particles is preferably 5 m ² / g or more, and more preferably 7 m ² / g or more.
When the specific surface area is 5 m ² / g or more, coarsening of the positive electrode active material particles can be suppressed, and the diffusion rate of lithium in the particles can be increased. Thereby, the battery characteristic of a lithium ion secondary battery can be improved.
The upper limit of the specific surface area of the positive electrode active material particles is not particularly limited as long as a desired effect is obtained, and may be 50 m ² / g or less, or 20 m ² / g or less.

Further, the positive electrode of the present embodiment is used as a positive electrode of a lithium ion secondary battery using natural graphite as a negative electrode, and the battery voltage of the lithium lithium ion secondary battery at a current value of 2C in an environment of 60 ° C. After charging at a constant current until the voltage reaches 4.1 V and then discharging until the battery voltage reaches 2 V at a current value of 2 C, the lithium lithium ion secondary battery is The charging capacity when charging at constant current until the battery voltage reaches 4.1V at a current value of 2C is defined as charging capacity A, and then the discharging capacity when discharging until the battery voltage reaches 2V at a current value of 2C is discharged. When the capacity is B, the integrated value when the difference between the discharge capacity B and the charge capacity A in one cycle (discharge capacity B−charge capacity A) is integrated over 500 cycles is 100 mAh / g or less, and 1 cycle It is preferable le th discharge capacity B is 100 mAh / g or more.
Since the lithium ion secondary battery of this embodiment contains inorganic phosphate particles, the elution of transition metals from the positive electrode of this embodiment is suppressed, so the lithium ion secondary battery using natural graphite as the negative electrode is The integrated value when the difference between the discharge capacity B and the charge capacity A in one cycle (discharge capacity B−charge capacity A) is integrated over 500 cycles is 100 mAh / g or less, and the discharge capacity B in the first cycle is It is 100 mAh / g or more, has an excellent capacity retention rate, and is excellent in safety and long-term cycle characteristics.

[Method for producing positive electrode]
Although the manufacturing method of the positive electrode of this embodiment will not be restrict | limited especially if the positive electrode active material particle of this embodiment is used, It is preferable that it is a method which can form a positive mix layer on one main surface of a collector.
First, a method for producing positive electrode active material particles will be described.

(Method for producing positive electrode active material particles)
The positive electrode of this embodiment includes at least positive electrode active material particles.
The method for producing positive electrode active material particles in the present embodiment is selected from the group consisting of, for example, a production process of positive electrode active material particles and positive electrode active material particle precursors, and positive electrode active material particles and positive electrode active material particle precursors. A slurry preparation step of preparing a slurry by mixing at least one positive electrode active material particle raw material, an organic compound that is a carbonaceous film precursor, and water; drying the slurry; and obtaining a dried product in a non-oxidizing atmosphere A firing step of firing below.

[Production Process of Positive Electrode Active Material Particles and Precursor of Positive Electrode Active Material Particles]
As a method for producing the compound represented by Li _x A _y M _z PO ₄ , conventional methods such as a solid phase method, a liquid phase method, and a gas phase method can be used. _{Examples of} Li _x A _y M _z PO ₄ obtained by such a method include particles (hereinafter sometimes referred to as “Li _x A _y M _z PO ₄ particles”).
For example, Li _x A _y M _z PO ₄ particles are hydrothermally synthesized from a slurry mixture obtained by mixing a Li source, an A source, a P source, water, and an M source as required. Is obtained. According to hydrothermal synthesis, Li _x A _y M _z PO ₄ is produced as a precipitate in water. Precipitate obtained _may be a precursor of _{Li x A y M z PO 4} . In this _case, by firing the precursor of _{Li x A y M z PO 4} , Li x A y M z PO 4 particles of interest are obtained.
It is preferable to use a pressure-resistant airtight container for this hydrothermal synthesis.

Here, examples of the Li source include lithium salts such as lithium acetate (LiCH ₃ COO) and lithium chloride (LiCl), and lithium hydroxide (LiOH). Among these, as the Li source, it is preferable to use at least one selected from the group consisting of lithium acetate, lithium chloride, and lithium hydroxide.

Examples of the A source include chlorides, carboxylates and sulfates containing at least one selected from the group consisting of Fe, Mn, Co and Ni. For _example, if A in Li _x A _y M z PO ₄ is Fe, as the Fe source, iron chloride (II) (FeCl _2), iron acetate _{(II) (Fe (CH 3} COO) 2), ferrous sulfate (II) Divalent iron salts such as (FeSO ₄ ) can be mentioned. Among these, as the Fe source, it is preferable to use at least one selected from the group consisting of iron (II) chloride, iron (II) acetate, and iron (II) sulfate.

  M source includes chloride, carboxylic acid containing at least one selected from the group consisting of Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge and rare earth elements Examples thereof include salts and sulfates.

Examples of the P source include phosphoric acid compounds such as phosphoric acid (H ₃ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ). . Among these, as the P source, it is preferable to use at least one selected from the group consisting of phosphoric acid, ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

[Slurry preparation process]
By the slurry preparation step, the organic compound as the carbonaceous film precursor is interposed between the positive electrode active material particles, and they are uniformly mixed, so that the surface of the positive electrode active material particles can be uniformly coated with the organic compound. .
Furthermore, the organic compound which coat | covers the surface of a positive electrode active material particle carbonizes by a baking process, and the positive electrode material containing the positive electrode active material particle by which the carbonaceous film was coat | covered uniformly is obtained.

  The organic compound used in the method for producing positive electrode active material particles in the present embodiment is not particularly limited as long as it is a compound that can form a carbonaceous film on the surface of the positive electrode active material particles. Examples of such organic compounds include polyvinyl alcohol (PVA), polyvinyl pyrrolidone, cellulose, starch, gelatin, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, polystyrene sulfonic acid, polyacrylamide, and polyvinyl acetate. Glucose, fructose, galactose, mannose, maltose, sucrose, lactose, glycogen, pectin, alginic acid, glucomannan, chitin, hyaluronic acid, chondroitin, agarose, polyether, ethylene glycol and other dihydric alcohols, glycerin and other trihydric alcohols Etc.

In the slurry preparation step, the positive electrode active material particle raw material and the organic compound are dissolved or dispersed in water to prepare a uniform slurry.
When these raw materials are dissolved or dispersed in water, a dispersant can be added.
The method for dissolving or dispersing the positive electrode active material particle raw material and the organic compound in water is not particularly limited as long as the positive electrode active material particle raw material is dispersed in water and the organic compound is dissolved or dispersed in water. . As such a method, for example, a method using a medium stirring type dispersion device that stirs medium particles at high speed, such as a planetary ball mill, a vibration ball mill, a bead mill, a paint shaker, and an attritor, is preferable.

  When the positive electrode active material particle raw material and the organic compound are dissolved or dispersed in water, the positive electrode active material particle raw material is dispersed as primary particles in water, and then the organic compound is added to the water and dissolved or dispersed. It is preferable to stir like this. If it does in this way, the surface of the primary particle of positive electrode active material particle raw material will be easily coat | covered with an organic compound. Thereby, the organic compound is uniformly arranged on the surface of the primary particles of the positive electrode active material particle raw material, and as a result, the surface of the primary particles of the positive electrode active material particles is covered with the carbonaceous film derived from the organic compound.

[Baking process]
Next, the slurry prepared in the slurry preparation step is sprayed and dried in a high temperature atmosphere, for example, in an atmosphere of 70 ° C. or higher and 250 ° C. or lower.
Next, the obtained dried product is calcined in a non-oxidizing atmosphere, preferably at a temperature of 500 ° C. or more and 1000 ° C. or less, more preferably at a temperature of 600 ° C. or more and 1000 ° C. or less for 0.1 hours or more and 40 hours or less. To do.

As the non-oxidizing atmosphere, an atmosphere made of an inert gas such as nitrogen (N ₂ ) or argon (Ar) is preferable. When it is desired to further suppress the oxidation of the dried product, a reducing atmosphere containing about several volume% of a reducing gas such as hydrogen (H ₂ ) is preferable. Further, for the purpose of removing organic components evaporated in the non-oxidizing atmosphere at the time of firing, a flammable gas such as oxygen (O ₂ ) or a combustible gas may be introduced into the non-oxidizing atmosphere.

  Here, by setting the firing temperature to 500 ° C. or higher, the decomposition and reaction of the organic compound contained in the dried product is likely to proceed sufficiently, and the organic compound is easily carbonized. As a result, it is easy to prevent the decomposition product of the high-resistance organic compound from being formed in the obtained aggregate. On the other hand, by setting the firing temperature to 1000 ° C. or less, lithium (Li) in the positive electrode active material particle raw material hardly evaporates, and the positive electrode active material particles are prevented from growing beyond the target size. . As a result, when a lithium ion secondary battery including a positive electrode including the positive electrode material of the present embodiment is manufactured, it is possible to prevent the discharge capacity at a high speed charge / discharge rate from being lowered, and lithium having sufficient charge / discharge rate performance. An ion secondary battery can be realized.

  As described above, the positive electrode active material particles in which the surfaces of the primary particles of the positive electrode active material particles are coated with carbon (carbonaceous film) generated by thermal decomposition of the organic compound in the dried product are obtained.

As described above, the lithium ion secondary battery of this embodiment is characterized by containing inorganic phosphate particles. The inorganic phosphate particles may be contained in the positive electrode mixture layer, may be present between the positive electrode mixture layer and the separator, may be supported on the separator, or may be contained in the electrolyte. It may be contained, may be contained in the negative electrode mixture layer, and may be contained in one or more places.
When the positive electrode contains inorganic phosphate particles, even if the positive electrode active material particles and inorganic phosphate particles are mixed before preparing the positive electrode material paste, the positive electrode active material particles and the inorganic Acid salt particles may be mixed.
The method of mixing the positive electrode active material particles and the inorganic phosphate particles is not particularly limited as long as the positive electrode active material particles and the inorganic phosphate particles can be uniformly mixed, but before preparing the positive electrode material paste, When mixing the active material particles and the inorganic phosphate particles, it is preferable to use a mixing method using an air flow because damage to the positive electrode active material particles (center particles, primary particles) can be suppressed. Moreover, in order to prevent the adsorption | suction of the water | moisture content to positive electrode active material particle | grains and inorganic phosphate particle | grains, mixing by the airflow using dry air, dry inert gas, etc. is more preferable.

(Preparation of positive electrode material paste)
As a method for producing the positive electrode of the present embodiment, for example, a positive electrode material paste including the positive electrode active material particles of the present embodiment, a binder composed of a binder resin, and a solvent are mixed to prepare a positive electrode material paste. At this time, the positive electrode material may be a mixture of positive electrode active material particles and inorganic phosphate particles, and the positive electrode material paste in the present embodiment may include a conductive material such as carbon black, if necessary. An auxiliary agent or inorganic phosphate particles may be added.

[Binder for preparing positive electrode material paste]
As the binder, that is, a binder resin, for example, polytetrafluoroethylene (PTFE) resin, polyvinylidene fluoride (PVdF) resin, fluororubber, and the like are preferably used.

The blending amount of the binder used in preparing the positive electrode material paste is not particularly limited. For example, it is 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the positive electrode material for a lithium ion secondary battery. It is preferably 3 parts by mass or more and 20 parts by mass or less.
When the blending amount of the binder is 1 part by mass or more, the binding property between the positive electrode mixture layer and the current collector can be sufficiently increased. Thereby, it is possible to prevent the positive electrode mixture layer from cracking or falling off during rolling of the positive electrode mixture layer. Moreover, in the charging / discharging process of a lithium ion secondary battery, it can suppress that a positive mix layer peels from a collector, and battery capacity and a charging / discharging rate fall. On the other hand, when the blending amount of the binder is 30 parts by mass or less, the internal resistance of the positive electrode material for a lithium ion secondary battery is reduced, and the battery capacity at a high-speed charge / discharge rate can be suppressed from decreasing.

[Conductive aid]
Although it does not specifically limit as a conductive support agent, For example, the group which consists of fibrous carbon, such as acetylene black (AB), ketjen black, furnace black, vapor growth carbon fiber (VGCF; Vapor Grown Carbon Fiber), and a carbon nanotube At least one selected from is used.

[Solvent for preparing positive electrode material paste]
The solvent used for the positive electrode material paste containing the positive electrode active material particles of the present embodiment is appropriately selected according to the properties of the binder. By appropriately selecting the solvent, the positive electrode material paste can be easily applied to an object to be coated such as a current collector.
Examples of the solvent include water; alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol: IPA), butanol, pentanol, hexanol, octanol, and diacetone alcohol; ethyl acetate, butyl acetate, and lactic acid. Esters such as ethyl, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate and γ-butyrolactone; diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol Acetates such as monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether and diethylene glycol monoethyl ether Ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), acetylacetone and cyclohexanone; amides such as dimethylformamide, N, N-dimethylacetoacetamide and N-methyl-2-pyrrolidone (NMP) And glycols such as ethylene glycol, diethylene glycol and propylene glycol. These solvents may be used alone or in a combination of two or more.

The content of the solvent in the positive electrode material paste is preferably 50% by mass or more and 70% by mass or less when the total mass of the positive electrode active material particles, the binder, and the solvent of the present embodiment is 100% by mass. More preferably, they are 55 mass% or more and 65 mass% or less.
When the content of the solvent in the positive electrode material paste is within the above range, a positive electrode material paste having excellent positive electrode forming properties and excellent battery characteristics can be obtained.

  As a method of mixing the positive electrode material including the positive electrode active material particles of this embodiment, the binder, the conductive additive, the inorganic phosphate particles, and the solvent, a method that can uniformly mix these components. If there is no particular limitation. Examples thereof include a mixing method using a kneading machine such as a ball mill, a sand mill, a planetary (planetary) mixer, a paint shaker, and a homogenizer.

The positive electrode material paste is applied to one main surface of the current collector to form a coating film, and then the coating film is dried to form a coating film composed of a mixture of the positive electrode material and the binder on the one main surface. Current collector is obtained.
Thereafter, the coating film is pressure-bonded and dried to produce a positive electrode having a positive electrode mixture layer on one main surface of the current collector.

[Inorganic phosphate particle layer]
In the lithium ion secondary battery of the present embodiment, inorganic phosphate particles may be contained in addition to the positive electrode. For example, an inorganic phosphate particle layer may be formed on the positive electrode mixture layer.

(Preparation of inorganic phosphate particle paste)
As a manufacturing method of the inorganic phosphate particle layer of the present embodiment, for example, the inorganic phosphate particles of the present embodiment, a binder composed of a binder resin, and a solvent are mixed to form inorganic phosphate particles. Prepare paste.

[Binder for preparing inorganic phosphate particle paste]
As the binder, that is, a binder resin, for example, polytetrafluoroethylene (PTFE) resin, polyvinylidene fluoride (PVdF) resin, fluororubber, and the like are preferably used.

The blending amount of the binder used in preparing the inorganic phosphate particle paste is not particularly limited. For example, it is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the inorganic phosphate particles. More preferably, it is 3 parts by mass or more and 20 parts by mass or less.
When the amount of the binder is 1 part by mass or more, the binding property between the inorganic phosphate particles can be sufficiently increased. Thereby, it is possible to prevent the inorganic phosphate particle layer from being cracked or dropped off during rolling of the inorganic phosphate particle layer. On the other hand, when the compounding amount of the binder is 30 parts by mass or less, it is possible to reduce the liquid resistance derived from the ion migration between the positive electrode and the negative electrode, and to suppress the battery capacity at the high speed charge / discharge rate from being lowered.

[Solvent for preparing inorganic phosphate particle paste]
The solvent used for the inorganic phosphate particle paste containing the inorganic phosphate particles of the present embodiment is appropriately selected according to the properties of the binder. By appropriately selecting the solvent, the positive electrode material paste can be easily applied to an object to be coated such as a current collector.
Examples of the solvent include water; alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol: IPA), butanol, pentanol, hexanol, octanol, and diacetone alcohol; ethyl acetate, butyl acetate, and lactic acid. Esters such as ethyl, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate and γ-butyrolactone; diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol Acetates such as monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether and diethylene glycol monoethyl ether Ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), acetylacetone and cyclohexanone; amides such as dimethylformamide, N, N-dimethylacetoacetamide and N-methyl-2-pyrrolidone (NMP) And glycols such as ethylene glycol, diethylene glycol and propylene glycol. These solvents may be used alone or in a combination of two or more.

The content of the solvent in the inorganic phosphate particle paste is 50% by mass or more and 70% by mass or less when the total mass of the inorganic phosphate particles, the binder, and the solvent of the present embodiment is 100% by mass. It is preferable that it is 55 mass% or more and 65 mass% or less.
If the content of the solvent in the inorganic phosphate particle paste is within the above range, the inorganic phosphate particle layer formability is excellent and the inorganic phosphate particles and the binder are easily dispersed uniformly. The transition metal eluted from the can be efficiently captured.

  A method of mixing the inorganic phosphate particles, the binder, and the solvent is not particularly limited as long as these components can be mixed uniformly. Examples thereof include a mixing method using a kneading machine such as a ball mill, a sand mill, a planetary (planetary) mixer, a paint shaker, and a homogenizer.

The inorganic phosphate particle paste is applied to the positive electrode mixture layer to form a coating film, and then the coating film is dried to form a coating film composed of a mixture of the above inorganic phosphate particles and the binder. It is formed on the agent layer.
Thereafter, the coating is pressure-bonded and dried, and has a positive electrode mixture layer on one main surface of the current collector, and a positive electrode / inorganic phosphor having an inorganic phosphate particle paste on the positive electrode mixture layer An acid salt particle layer is prepared.

[Negative electrode]
As the negative electrode, for example, a metal Li, natural graphite, carbon materials such as hard carbon, include those containing an anode material such as Li alloys and _{Li 4 Ti 5 O 12, Si} (Li 4.4 Si).
The negative electrode material can contain inorganic phosphate particles. When the negative electrode material includes inorganic phosphate particles, the content of the inorganic phosphate particles in the negative electrode material can be 0.1 mass% or more and 10 mass% or less, 0.2 mass% or more and It is preferably 10% by mass or less, more preferably 0.4% by mass or more and 7% by mass or less, and further preferably 0.5% by mass or more and 7% by mass or less.

〔Electrolytes〕
The electrolyte is not particularly limited, but is preferably a non-aqueous electrolyte. For example, ethylene carbonate (ethylene carbonate; EC) and ethyl methyl carbonate (ethyl methyl carbonate; EMC) have a volume ratio of 1: 1. In this manner, lithium hexafluorophosphate (LiPF ₆ ) is dissolved in the obtained mixed solvent so as to have a concentration of 1 mol / dm 3, for example.
The electrolyte can contain inorganic phosphate particles. When the electrolyte includes inorganic phosphate particles, the content of the inorganic phosphate particles in the electrolyte can be 0.02% by mass or more and 1.2% by mass or less with respect to the mass of the electrolyte. It is preferable that they are 0.04 mass% or more and 0.8 mass% or less. When the content is 0.02% by mass or more, the transition metal eluted from the positive electrode can be efficiently captured, and when the content is 1.2% by mass or less, the liquid resistance derived from ion migration between the positive electrode and the negative electrode can be reduced.

[Separator]
For example, porous propylene can be used as the separator.
A solid electrolyte may be used instead of the nonaqueous electrolyte and the separator.

When the lithium ion secondary battery of the present embodiment includes the positive electrode for the lithium ion secondary battery of the present embodiment as the positive electrode, the oxidative decomposition of the electrolyte and the generation of gas are suppressed, and the stability and safety of the long-term cycle Excellent.
The separator can contain inorganic phosphate particles. When the separator includes inorganic phosphate particles, the content of the inorganic phosphate particles in the separator can be 0.5% by mass or more and 30% by mass or less, and 1% by mass or more and 20% by mass or less. It is preferable that If it is 0.5% by mass or more, the transition metal eluted from the positive electrode can be efficiently captured, and if it is 30% by mass or less, the liquid resistance derived from ion migration between the positive electrode and the negative electrode can be reduced.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to a following example.

<Example 1>
[Synthesis of positive electrode active material particles]
In 2 L (liter) of water, 2 mol of lithium phosphate (Li ₃ PO ₄ ) and 2 mol of iron (II) sulfate (FeSO ₄ ) were mixed so that the total amount was 4 L (liter). A slurry mixture was prepared. The obtained mixture was accommodated in a pressure-resistant airtight container having a capacity of 8 L (liter) and hydrothermally synthesized at 180 ° C. for 1 hour to produce a precipitate. The obtained precipitate was washed with water to obtain a precursor of cake-like positive electrode active material particles.
Next, 5.5 g of polyethylene glycol as an organic compound and 500 g of zirconia balls having a diameter of 5 mm as medium particles are mixed with 150 g of the positive electrode active material particle precursor (in terms of solid content) for 12 hours using a ball mill. Dispersion treatment was performed to prepare a uniform slurry. The prepared slurry was sprayed into an air atmosphere at 180 ° C. and dried to obtain a granulated body composed of LiFePO ₄ coated with an organic compound having an average particle diameter of 6 μm.
The obtained granulated body was calcined in a non-oxidizing gas atmosphere at 700 ° C. for 1 hour and then held at 40 ° C. for 30 minutes to obtain LiFePO ₄ (positive electrode active material particles A1) having a conductive carbonaceous coating. ) The average primary particle diameter of the positive electrode active material particles A1 was 150 nm.
The average primary particle diameter of the positive electrode active material particles is measured by averaging the lengths of the long sides of 100 randomly selected primary particles in an image taken with a scanning electron microscope (SEM). The average primary particle diameter (D50) of the inorganic phosphate particles was measured by using Horiba, Ltd., LB-550, and Horiba, Ltd., SZ-100.

[Synthesis of inorganic phosphate particles]
In 500 mL (milliliter) of water, 0.5 mol of phosphoric acid (H ₃ PO ₄ ) and 0.5 mol of lithium carbonate (Li ₂ CO ₃ ) were mixed to prepare a mixture on a uniform slurry. The prepared mixture was heated at 150 ° C. overnight to evaporate moisture and dry the mixture. The dried mixture was baked in an air atmosphere at 600 ° C. for 12 hours to obtain inorganic phosphate particles made of Li ₄ P ₂ O ₇ .
Subsequently, the obtained inorganic phosphate particles were classified with a stainless steel sieve having an opening of 45 μm to obtain Li ₄ P ₂ O ₇ (inorganic phosphate particles B1) having a particle diameter of 45 μm or less.
The average primary particle diameter of the inorganic phosphate particles B1 was 18 μm.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
The positive electrode active material particles A1 and the inorganic phosphate particles B1 are combined with the mass of the inorganic phosphate particles B1 with respect to the positive electrode active material particles A1 (100 parts by mass). The amount obtained in the column “Amount” is 5.3 parts by mass, and the obtained powder was used as the positive electrode material (positive electrode material C1) for the lithium ion secondary battery of Example 1.

[Production of lithium ion secondary battery]
Mass in paste of N-methyl-2-pyrrolidinone (NMP) as a solvent, positive electrode material C1, polyvinylidene fluoride (PVdF) as a binder, and acetylene black (AB) as a conductive additive. In addition, the positive electrode material C1: AB: PVdF = 90: 5: 5 was added, and these were mixed to prepare a positive electrode material paste (for positive electrode).
The prepared positive electrode material paste (for positive electrode) is applied to the surface of an aluminum foil (current collector) having a thickness of 30 μm to form a coating film, the coating film is dried, and a positive electrode mixture layer is formed on the surface of the aluminum foil. Formed. The thickness of the positive electrode mixture layer was adjusted so that the capacity ratio of the positive electrode to the negative electrode was 1.2 (negative electrode / positive electrode).
Thereafter, the positive electrode mixture layer was pressurized at a predetermined pressure so that the positive electrode density was 2.0 g / mL, and then punched into a square shape having a positive electrode area of 9 cm ² using a molding machine. A positive electrode was produced.

Next, natural water as a negative electrode active material, styrene butadiene latex (SBR) as a binder, and carboxymethylcellulose (CMC) as a viscosity modifier are mixed in pure water as a solvent in a mass ratio of the paste. Graphite: SBR: CMC = 98: 1: 1 were added, and these were mixed to prepare a negative electrode material paste (for negative electrode).
The prepared negative electrode material paste (for negative electrode) is applied to the surface of a 10 μm thick copper foil (current collector) to form a coating film, the coating film is dried, and a negative electrode mixture layer is formed on the copper foil surface. Formed. The coating thickness was adjusted so that the basis weight of the negative electrode mixture layer was 4.4 mg / cm ² . After pressurizing at a predetermined pressure so that the negative electrode density was 1.42 g / mL, a negative electrode area of 9.6 cm ² was punched out using a molding machine to produce the negative electrode of Example 1.

The produced positive electrode and negative electrode were opposed to each other through a 25 μm thick separator made of polypropylene, impregnated with 0.5 mL of 1M LiPF ₆ solution as an electrolyte, and then sealed with a laminate film. 1 lithium ion secondary battery was produced. The LiPF ₆ solution used was a mixture of ethylene carbonate and ethyl methyl carbonate so that the volume ratio was 1: 1.

<Example 2>
[Synthesis of positive electrode active material particles]
Example 2 positive electrode active material particles A2 were obtained in the same manner as Example 1.
[Synthesis of inorganic phosphate particles]
In the same manner as in Example 1, inorganic phosphate particles B2 of Example 2 were obtained.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
Positive electrode active material particles A2 and inorganic phosphate particles B2 are uniformly mixed so that the mass of inorganic phosphate particles B2 with respect to positive electrode active material particles A2 (100 parts by mass) is 1 part by mass. Was used as the positive electrode material (positive electrode material C2) for the lithium ion secondary battery of Example 2.

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 2 was produced in the same manner as Example 1 except that the positive electrode material C2 of Example 2 was used instead of the positive electrode material C1.

<Example 3>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A3 of Example 3 were obtained.

[Synthesis of inorganic phosphate particles]
In 500 mL (milliliter) of water, 0.5 mol of phosphoric acid (H ₃ PO ₄ ) and 0.75 mol of lithium carbonate (Li ₂ CO ₃ ) were mixed to prepare a mixture on a uniform slurry. The prepared mixture was heated at 150 ° C. overnight to evaporate moisture and dry the mixture. The dried mixture was baked in an air atmosphere at 600 ° C. for 12 hours to obtain inorganic phosphate particles made of Li ₃ PO ₄ .
Subsequently, the obtained inorganic phosphate particles were classified with a stainless steel sieve having an opening of 45 μm to obtain Li ₃ PO ₄ (inorganic phosphate particles B3) having a particle diameter of 45 μm or less.
The average primary particle diameter of the inorganic phosphate particles B3 was 27 μm.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
The positive electrode active material particles A3 and the inorganic phosphate particles B3 are uniformly mixed so that the mass of the inorganic phosphate particles B3 with respect to the positive electrode active material particles A3 (100 parts by mass) is 5.3 parts by mass. The powder was used as a positive electrode material for a lithium ion secondary battery of Example 3 (positive electrode material C3).

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 3 was produced in the same manner as in Example 1 except that the positive electrode material C3 of Example 3 was used instead of the positive electrode material C1.

<Example 4>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A4 of Example 4 were obtained.
[Synthesis of inorganic phosphate particles]
In the same manner as in Example 3, inorganic phosphate particles B4 of Example 4 were obtained.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
Positive electrode active material particles A4 and inorganic phosphate particles B4 are uniformly mixed so that the mass of the inorganic phosphate particles B4 with respect to the positive electrode active material particles A4 (100 parts by mass) is 1 part by mass. Was used as the positive electrode material (positive electrode material C4) for the lithium ion secondary battery of Example 4.

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 4 was produced in the same manner as in Example 1 except that the positive electrode material C4 of Example 4 was used instead of the positive electrode material C1.

<Example 5>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A5 of Example 5 were obtained.

[Synthesis of inorganic phosphate particles]
In 500 mL (milliliter) of water, 0.5 mol of phosphoric acid (H ₃ PO ₄ ) and 0.17 mol of lithium citrate (Li ₃ C ₆ H ₅ O ₇ ) are mixed, and the mixture on the uniform slurry is mixed. Prepared. The prepared mixture was heated at 150 ° C. overnight to evaporate moisture and dry the mixture. The dried mixture was baked in a non-oxidizing atmosphere at 600 ° C. for 12 hours to obtain inorganic phosphate particles made of LiPO ₃ .
Subsequently, the obtained inorganic phosphate particles were classified with a stainless steel sieve having an opening of 45 μm to obtain LiPO ₃ (inorganic phosphate particles B5) having a particle size of 45 μm or less.
The average primary particle diameter of the inorganic phosphate particles B5 was 21 μm.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
The positive electrode active material particles A5 and the inorganic phosphate particles B5 are uniformly mixed so that the mass of the inorganic phosphate particles B5 with respect to the positive electrode active material particles A5 (100 parts by mass) is 5.3 parts by mass. The powder was used as a positive electrode material for a lithium ion secondary battery of Example 5 (positive electrode material C5).

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 5 was produced in the same manner as in Example 1 except that the positive electrode material C5 of Example 5 was used instead of the positive electrode material C1.

<Example 6>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A6 of Example 6 were obtained.

[Synthesis of inorganic phosphate particles]
In the same manner as in Example 5, inorganic phosphate particles B6 of Example 6 were obtained.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
Positive electrode active material particles A6 and inorganic phosphate particles B6 are uniformly mixed so that the mass of inorganic phosphate particles B6 with respect to positive electrode active material particles A6 (100 parts by mass) is 1 part by mass. Was used as the positive electrode material (positive electrode material C6) for the lithium ion secondary battery of Example 6.

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 6 was produced in the same manner as in Example 1 except that the positive electrode material C6 of Example 6 was used instead of the positive electrode material C1.

<Example 7>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A7 of Example 7 were obtained.

[Synthesis of inorganic phosphate particles]
In 500 mL (milliliter) of water, 0.5 mol of phosphoric acid (H ₃ PO ₄ ) and 0.25 mol of lithium carbonate (Li ₂ CO ₃ ) were mixed to prepare a mixture on a uniform slurry. The prepared mixture was heated at 150 ° C. overnight to evaporate moisture and dry the mixture. The dried mixture was baked in an air atmosphere at 800 ° C. for 12 hours to obtain inorganic phosphate particles made of amorphous LiPO ₃ .
Subsequently, the obtained inorganic phosphate particles were classified with a stainless steel sieve having an opening of 45 μm to obtain amorphous LiPO ₃ (inorganic phosphate particles B7) having a particle size of 45 μm or less.
The average primary particle diameter of the inorganic phosphate particles B7 was 13 μm.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
The positive electrode active material particles A7 and the inorganic phosphate particles B7 are uniformly mixed so that the mass of the inorganic phosphate particles B7 with respect to the positive electrode active material particles A7 (100 parts by mass) is 5.3 parts by mass. The obtained powder was used as a positive electrode material for a lithium ion secondary battery of Example 7 (positive electrode material C7).

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 7 was produced in the same manner as Example 1 except that the positive electrode material C7 of Example 7 was used instead of the positive electrode material C1.

<Example 8>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A8 of Example 8 were obtained.
[Synthesis of inorganic phosphate particles]
In the same manner as in Example 7, inorganic phosphate particles B8 of Example 8 were obtained.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
Positive electrode active material particles A8 and inorganic phosphate particles B8 are uniformly mixed so that the mass of inorganic phosphate particles B8 with respect to positive electrode active material particles A8 (100 parts by mass) is 1 part by mass. Was used as the positive electrode material for the lithium ion secondary battery of Example 8 (positive electrode material C8).

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 8 was produced in the same manner as Example 1 except that the positive electrode material C8 of Example 8 was used instead of the positive electrode material C1.

<Example 9>
[Synthesis of positive electrode active material particles]
In 2 L (liter) of water, 2 mol of lithium phosphate (Li ₃ PO ₄ ), 1.4 mol of manganese (II) sulfate (MnSO ₄ ), and 0.6 mol of iron (II) sulfate (FeSO ₄ ) The mixture was mixed so that the total amount was 4 L (liter) to prepare a uniform slurry mixture. The prepared mixture was housed in a pressure-resistant airtight container having a capacity of 8 L (liter), and hydrothermally synthesized at 180 ° C. for 1 hour to produce a precipitate. The produced precipitate was washed with water to obtain a cake-like positive electrode active material precursor.
To the obtained positive electrode active material precursor 150 g (in terms of solid content), 5.5 g of polyethylene glycol as an organic compound and 500 g of zirconia balls having a diameter of 5 mm as medium particles are mixed and dispersed for 12 hours in a ball mill. Processing was performed to prepare a uniform slurry.
The prepared slurry was sprayed into an air atmosphere at 180 ° C. and dried to obtain a granulated body composed of LiMn _0.7 Fe _0.3 PO ₄ coated with an organic compound having an average particle diameter of 6 μm. .
The obtained granulated body was fired in a non-oxidizing gas atmosphere at 700 ° C. for 1 hour, then held at 40 ° C. for 30 minutes, and LiMn _0.7 Fe _0.3 PO ₄ having a conductive carbon coating. (Positive electrode active material particles A9) were obtained.
The average primary particle diameter of the positive electrode active material particles A9 was 100 nm.

[Synthesis of inorganic phosphate particles]
In the same manner as in Example 1, inorganic phosphate particles B9 of Example 9 were obtained.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
The positive electrode active material particles A9 and the inorganic phosphate particles B9 are uniformly mixed so that the mass of the inorganic phosphate particles B9 with respect to the positive electrode active material particles A9 (100 parts by mass) is 5.3 parts by mass. The powder was used as a positive electrode material for a lithium ion secondary battery of Example 9 (positive electrode material C9).

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 9 was produced in the same manner as in Example 1 except that the positive electrode material C9 of Example 9 was used instead of the positive electrode material C1.

<Example 10>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 9, positive electrode active material particles A10 of Example 10 were obtained.
[Synthesis of inorganic phosphate particles]
In the same manner as in Example 3, inorganic phosphate particles B10 of Example 10 were obtained.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
The positive electrode active material particles A10 and the inorganic phosphate particles B10 are uniformly mixed so that the mass of the inorganic phosphate particles B10 with respect to the positive electrode active material particles A10 (100 parts by mass) is 5.3 parts by mass. The obtained powder was used as a positive electrode material for a lithium ion secondary battery of Example 10 (positive electrode material C10).

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 10 was produced in the same manner as in Example 1 except that the positive electrode material C10 of Example 10 was used instead of the positive electrode material C1.

<Example 11>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 9, positive electrode active material particles A11 of Example 11 were obtained.
[Synthesis of inorganic phosphate particles]
In the same manner as in Example 5, inorganic phosphate particles B11 of Example 11 were obtained.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
The positive electrode active material particles A11 and the inorganic phosphate particles B11 are uniformly mixed so that the mass of the inorganic phosphate particles B11 with respect to the positive electrode active material particles A11 (100 parts by mass) is 5.3 parts by mass. The powder was used as a positive electrode material for a lithium ion secondary battery of Example 11 (positive electrode material C11).

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 11 was produced in the same manner as Example 1 except that the positive electrode material C11 of Example 11 was used instead of the positive electrode material C1.

<Example 12>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 9, positive electrode active material particles A12 of Example 12 were obtained.
In the same manner as in Example 7, inorganic phosphate particles B12 of Example 12 were obtained.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
The positive electrode active material particles A12 and the inorganic phosphate particles B12 are uniformly mixed so that the mass of the inorganic phosphate particles B12 with respect to the positive electrode active material particles A12 (100 parts by mass) is 5.3 parts by mass. The powder was used as a positive electrode material for a lithium ion secondary battery of Example 12 (positive electrode material C12).

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 12 was produced in the same manner as in Example 1 except that the positive electrode material C12 of Example 12 was used.

<Comparative Example 1>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A21 of Comparative Example 1 were obtained.

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Comparative Example 1 was produced in the same manner as Example 1 except that the positive electrode active material particles A21 of Comparative Example 1 were used as the positive electrode material instead of the positive electrode material C1.

<Comparative example 2>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 9, positive electrode active material particles A22 of Comparative Example 2 were obtained.

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Comparative Example 2 was produced in the same manner as Example 1 except that the positive electrode active material particles A22 of Comparative Example 2 were used as the positive electrode material instead of the positive electrode material C1.

<Example 13>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A23 of Example 13 were obtained.
[Synthesis of inorganic phosphate particles]
In the same manner as in Example 1, inorganic phosphate particles B23 of Example 13 were obtained.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
The positive electrode active material particles A23 and the inorganic phosphate particles B23 are uniformly mixed so that the mass of the inorganic phosphate particles B23 with respect to the positive electrode active material particles A23 (100 parts by mass) is 0.1 parts by mass. The powder was used as a positive electrode material for a lithium ion secondary battery of Example 13 (positive electrode material C23).

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 13 was produced in the same manner as in Example 1 except that the positive electrode material C23 of Example 13 was used instead of the positive electrode material C1.

<Example 14>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A24 of Example 14 were obtained.
[Synthesis of inorganic phosphate particles]
In the same manner as in Example 1, inorganic phosphate particles B24 of Example 14 were obtained.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
Obtained by uniformly mixing the positive electrode active material particles A24 and the inorganic phosphate particles B24 so that the mass of the inorganic phosphate particles B24 with respect to the positive electrode active material particles A24 (100 parts by mass) is 0.5 parts by mass. The powder was used as a positive electrode material for a lithium ion secondary battery of Example 14 (positive electrode material C24).

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 14 was produced in the same manner as in Example 1 except that the positive electrode material C24 of Example 14 was used instead of the positive electrode material C1.

<Example 15>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A25 of Example 15 were obtained.
[Synthesis of inorganic phosphate particles]
In the same manner as in Example 1, inorganic phosphate particles B25 of Example 15 were obtained.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
Positive electrode active material particles A25 and inorganic phosphate particles B25 are uniformly mixed so that the mass of inorganic phosphate particles B25 with respect to positive electrode active material particles A25 (100 parts by mass) is 3 parts by mass. Was used as the positive electrode material (positive electrode material C25) for the lithium ion secondary battery of Example 15.

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 15 was produced in the same manner as in Example 1 except that the positive electrode material C25 of Example 15 was used instead of the positive electrode material C1.

<Example 16>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A26 of Example 16 were obtained.
[Synthesis of inorganic phosphate particles]
In the same manner as in Example 1, inorganic phosphate particles B26 of Example 16 were obtained.

[Mixing of positive electrode active material particles and inorganic phosphate particles]
The positive electrode active material particles A26 and the inorganic phosphate particles B26 are uniformly mixed so that the mass of the inorganic phosphate particles B26 with respect to the positive electrode active material particles A26 (100 parts by mass) is 8.7 parts by mass. The powder was used as a positive electrode material for a lithium ion secondary battery of Example 16 (positive electrode material C26).

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Example 16 was produced in the same manner as in Example 1 except that the positive electrode material C26 of Example 16 was used instead of the positive electrode material C1.

< Reference Example 17>
[Synthesis of inorganic phosphate particles]
In the same manner as in Example 1, inorganic phosphate particles B27 of Reference Example 17 were obtained.

[Synthesis of positive electrode active material precursor]
In 2 L (liter) of water, 2 mol of lithium phosphate (Li ₃ PO ₄ ) and 2 mol of iron (II) sulfate (FeSO ₄ ) were mixed so that the total amount was 4 L (liter). A slurry mixture was prepared. The prepared mixture was housed in a pressure-resistant airtight container having a capacity of 8 L (liter), and hydrothermally synthesized at 180 ° C. for 1 hour to produce a precipitate. The produced precipitate was washed with water to obtain a cake-like positive electrode active material precursor.

[Synthesis of positive electrode active material particles and inorganic phosphate coating on the surface of the positive electrode active material particles]
To the obtained positive electrode active material precursor 150 g (in terms of solid content), 5.5 g of polyethylene glycol as an organic compound and 500 g of zirconia balls having a diameter of 5 mm as medium particles are mixed and dispersed for 12 hours in a ball mill. Processing was performed to prepare a uniform slurry. The prepared slurry was sprayed into an air atmosphere at 180 ° C. and dried to obtain a granulated body composed of LiFePO ₄ coated with an organic compound having an average particle diameter of 6 μm.
The obtained granulate and the inorganic phosphate particles B27 of Reference Example 17 were mixed, and the resulting mixture was fired in a non-oxidizing gas atmosphere at 700 ° C. for 1 hour, and then at 40 ° C. for 30 minutes. LiFePO ₄ (positive electrode active material particles A27) having a conductive carbonaceous coating and an inorganic phosphate coating was obtained.
The average primary particle diameter of the positive electrode active material particles A27 was 160 nm.

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Reference Example 17 was produced in the same manner as in Example 1 except that the positive electrode active material particles A27 of Reference Example 17 were used as the positive electrode material instead of the positive electrode material C1.

< Reference Example 18>
[Synthesis of positive electrode active material precursor]
In 2 L (liter) of water, 2 mol of lithium phosphate (Li ₃ PO ₄ ) and 2 mol of iron (II) sulfate (FeSO ₄ ) were mixed so that the total amount was 4 L (liter). A slurry mixture was prepared. The prepared mixture was housed in a pressure-resistant airtight container having a capacity of 8 L (liter), and hydrothermally synthesized at 180 ° C. for 1 hour to produce a precipitate. The produced precipitate was washed with water to obtain a cake-like positive electrode active material precursor.

[Synthesis of positive electrode active material particles and inorganic phosphate coating on the surface of the positive electrode active material particles]
The obtained positive electrode active material precursor 150 g (in terms of solid content), 5.5 g of polyethylene glycol as the organic compound, phosphoric acid aqueous solution containing 9.31 g of phosphoric acid (H ₃ PO ₄ ), lithium carbonate (Li ₂ CO ₃ ) 7.02 g and 500 g of zirconia balls having a diameter of 5 mm as medium particles were mixed and dispersed in a ball mill for 12 hours to prepare a uniform slurry.
The prepared slurry was sprayed into an air atmosphere at 180 ° C. and dried to obtain a granulated body composed of LiFePO ₄ coated with an organic compound having an average particle diameter of 6 μm.
The obtained granulated body was fired in a non-oxidizing gas atmosphere at 700 ° C. for 1 hour and then held at 40 ° C. for 30 minutes, and LiFePO ₄ having a conductive carbonaceous coating and an inorganic phosphate coating. (Positive electrode active material particles A28) were obtained.
The average primary particle diameter of the positive electrode active material particles A28 was 180 nm.

[Production of lithium ion secondary battery]
A lithium ion secondary battery of Reference Example 18 was produced in the same manner as Example 1 except that the positive electrode active material particles A28 of Reference Example 18 were used as the positive electrode material instead of the positive electrode material C1.

<Example 19>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A29 of Example 19 were obtained.
[Synthesis of inorganic phosphate particles]
In the same manner as in Example 1, inorganic phosphate particles B29 of Example 19 were obtained.

[Production of lithium ion secondary battery]
N-methyl-2-pyrrolidinone (NMP) as a solvent, positive electrode active material particles A27, inorganic phosphate particles B27, polyvinylidene fluoride (PVdF) as a binder, and acetylene black as a conductive auxiliary agent (AB) is added so that the positive electrode active material A29: inorganic phosphate particles B29: AB: PVdF = 85.5: 4.5: 5: 5 in a mass ratio in the paste, and these are mixed. Then, a lithium ion secondary battery of Example 19 was produced in the same manner as Example 1 except that the positive electrode material paste (for positive electrode) was prepared.

<Example 20>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A30 of Example 20 were obtained.
[Synthesis of inorganic phosphate particles]
In 500 mL (milliliter) of water, 0.5 mol of phosphoric acid (H ₃ PO ₄ ) and 0.5 mol of lithium carbonate (Li ₂ CO ₃ ) were mixed to prepare a mixture on a uniform slurry. The prepared mixture was heated at 150 ° C. overnight to evaporate moisture and dry the mixture. The dried mixture was baked in an air atmosphere at 600 ° C. for 12 hours to obtain inorganic phosphate particles made of Li ₄ P ₂ O ₇ .
Next, 50 g of the obtained inorganic phosphate particles, 50 g of pure water, and 500 g of zirconia balls having a diameter of 5 mm as medium particles were mixed, and pulverized for 6 hours in a ball mill. Fine inorganic phosphate particles were obtained by drying in an air atmosphere for 12 hours.
Subsequently, the obtained fine inorganic phosphate particles were classified with a stainless steel sieve having an opening of 45 μm to obtain Li ₄ P ₂ O ₇ (inorganic phosphate particles B30) having a particle diameter of 45 μm or less.
The average primary particle diameter of the inorganic phosphate particles B30 was 3 μm.

[Production of lithium ion secondary battery]
A positive electrode of Example 20 was produced in the same manner as in Example 1 except that the positive electrode active material particles A30 of Example 20 were used as the positive electrode material instead of the positive electrode material C1.
Next, N-methyl-2-pyrrolidinone (NMP) as a solvent, inorganic phosphate particles B30, and polyvinylidene fluoride (PVdF) as a binder at a mass ratio in the paste, inorganic phosphoric acid In addition to adding salt particles B30: PVdF = 95: 5, these were mixed to prepare an inorganic phosphate particle paste (for inorganic phosphate particle layer).
Next, an inorganic phosphate particle paste is applied on the surface of the positive electrode on which the positive electrode mixture layer is formed, a coating film is formed, the coating film is dried, and inorganic phosphate particles are formed on the surface of the positive electrode mixture layer. A layer was formed. Subsequently, the obtained positive electrode mixture layer / inorganic phosphate particle layer was pressurized. The coating amount of the inorganic phosphate particle paste was adjusted so that the thickness of the inorganic phosphate layer after pressurization was 3 μm. The mass% of the inorganic phosphate particles B30 with respect to the positive electrode active material A30 was 6.8%.
Next, in the same manner as in Example 1, a negative electrode of Example 20 was produced.

The positive electrode having the inorganic phosphate particle layer formed on the surface of the prepared positive electrode mixture layer and the negative electrode are opposed to each other through a 25 μm thick separator made of polypropylene, and 0.5 mL of 1M LiPF ₆ solution as an electrolyte After being impregnated with, a lithium ion secondary battery of Example 1 was produced by sealing with a laminate film. The LiPF ₆ solution used was a mixture of ethylene carbonate and ethyl methyl carbonate so that the volume ratio was 1: 1.

<Example 21>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A31 of Example 21 were obtained.
[Synthesis of inorganic phosphate particles]
In the same manner as in Example 1, inorganic phosphate particles B31 of Example 21 were obtained.

[Production of lithium ion secondary battery]
A positive electrode of Example 21 was produced in the same manner as in Example 1 except that the positive electrode active material particles A31 of Example 21 were used as the positive electrode material instead of the positive electrode material C1.
Next, in the same manner as in Example 1, a negative electrode of Example 21 was produced.

Next, inorganic phosphate particles B31 were mixed in a 1M LiPF ₆ solution as an electrolyte so that the mass was 5.3% by mass with respect to the mass of the positive electrode active material A31. The LiPF ₆ solution used was a mixture of ethylene carbonate and ethyl methyl carbonate so that the volume ratio was 1: 1.
Next, the prepared positive electrode and negative electrode are opposed to each other with a separator made of polypropylene having a thickness of 25 μm, impregnated with an electrolyte mixed with the above-described inorganic phosphate particles, and then sealed with a laminate film, A lithium ion secondary battery of Example 21 was produced.

<Example 22>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A32 of Example 22 were obtained.
[Synthesis of inorganic phosphate particles]
In the same manner as in Example 20, inorganic phosphate particles B32 of Example 22 were obtained.

[Production of lithium ion secondary battery]
A positive electrode of Example 22 was produced in the same manner as in Example 1 except that the positive electrode active material particles A32 of Example 22 were used as the positive electrode material instead of the positive electrode material C1.
Next, in the same manner as in Example 1, a negative electrode of Example 22 was produced.

Subsequently, it mixed so that inorganic phosphate particle | grains B32 might be 20 mass% with respect to the pure water as a solvent, and prepared the inorganic phosphate particle solution. Next, after impregnating this inorganic phosphate particle solution with a separator made of polypropylene and having a thickness of 25 μm, the separator was taken out and dried under reduced pressure at 70 ° C. for 12 hours to carry the inorganic phosphate particles. Was made. The speed | rate which takes out a separator from an inorganic phosphate particle solution was adjusted so that the mass% of inorganic phosphate particle | grains B32 with respect to positive electrode active material A32 might be 5.3%.
The prepared positive electrode and negative electrode were opposed to each other through a separator carrying inorganic phosphate particles, impregnated with 0.5 mL of 1M LiPF ₆ solution as an electrolyte, and then sealed with a laminate film. The lithium ion secondary battery of Example 22 was produced. The LiPF ₆ solution used was a mixture of ethylene carbonate and ethyl methyl carbonate so that the volume ratio was 1: 1.

<Example 23>
[Synthesis of positive electrode active material particles]
In the same manner as in Example 1, positive electrode active material particles A33 of Example 23 were obtained.
[Synthesis of inorganic phosphate particles]
In the same manner as in Example 1, inorganic phosphate particles B33 of Example 23 were obtained.

[Production of lithium ion secondary battery]
A positive electrode of Example 23 was produced in the same manner as in Example 1 except that the positive electrode active material particles A33 of Example 23 were used as the positive electrode material instead of the positive electrode material C1.

Next, natural graphite as a negative electrode active material, inorganic phosphate particles B33, styrene butadiene latex (SBR) as a binder, and carboxymethyl cellulose (CMC) as a viscosity modifier in pure water as a solvent. , Natural graphite: inorganic phosphate particles: SBR: CMC = 90.5: 7.5: 1: 1, and these are mixed and mixed to obtain a negative electrode material paste (for negative electrode) Was prepared.
The prepared negative electrode material paste (for negative electrode) is applied to the surface of a 10 μm thick copper foil (current collector) to form a coating film, the coating film is dried, and a negative electrode mixture layer is formed on the copper foil surface. Formed. The coating thickness was adjusted so that the basis weight of the negative electrode mixture layer was 4.4 mg / cm ² . After pressurizing at a predetermined pressure such that the negative electrode density was 1.42 g / mL, a negative electrode area of 9.6 cm ² was punched out using a molding machine to produce a negative electrode of Example 23.

The produced positive electrode and negative electrode were opposed to each other through a 25 μm thick separator made of polypropylene, impregnated with 0.5 mL of 1M LiPF ₆ solution as an electrolyte, and then sealed with a laminate film. 23 lithium ion secondary batteries were produced. The LiPF ₆ solution used was a mixture of ethylene carbonate and ethyl methyl carbonate so that the volume ratio was 1: 1.

<Evaluation of lithium ion secondary battery>
About the lithium ion secondary battery of Examples 1-16, 19-23, Reference Examples 17-18, and Comparative Examples 1-2, the charging / discharging test and the overcharge test were done as follows.
(1) Cycle test Under a 60 ° C environment, a constant current charge is performed until the battery voltage reaches 4.1V at a current value of 2C, and then one cycle until the battery voltage is discharged until the battery voltage reaches 2V at a current value of 2C. age,
During the one cycle, the charge capacity at the time of constant current charging until the battery voltage becomes 4.1V at a current value of 2C is defined as a charge capacity A, and then discharged until the battery voltage becomes 2V at a current value of 2C. When the discharge capacity at the time is defined as the discharge capacity B, the integrated value when the difference between the discharge capacity B and the charge capacity A in one cycle (discharge capacity B−charge capacity A) is integrated over 500 cycles is evaluated as an irreversible capacity. The results are shown in Table 1.
The discharge capacity B at the first cycle was evaluated as the discharge capacity.
The ratio when the discharge capacity B at the first cycle was used as the denominator and the discharge capacity B at the 500th cycle was used as the numerator was evaluated as a capacity maintenance ratio.

(2) Negative electrode Fe quantitative test The laminate cell after the elapse of 500 cycles in the cycle test of (1) was opened in the atmosphere, the negative electrode was rinsed with 3 g of diethyl carbonate (DEC), and then dried under vacuum at 50 ° C. for 12 hours. I let you. Next, the graphite on the dried negative electrode was scraped off with a ceramic spatula to collect all the graphite on the negative electrode. Next, the recovered graphite was put in a platinum crucible, covered, and gradually heated to 700 ° C. in an electric furnace to ash the sample. Next, lithium tetraborate was added to the incinerated sample and heated to 925 ° C. in an electric furnace and melted. Next, the molten sample was placed in a tall beaker together with the platinum crucible, and hot water and nitric acid were added and dissolved by stirring. Using this dissolved solution as a test solution, the amount of Fe was measured by ICP-AES. The Fe ratio (Fe mass / total graphite mass on the negative electrode after 500 cycles) in the obtained negative electrode was evaluated as the negative electrode Fe amount [mg / kg].

<Evaluation results>
Table 1 shows the evaluation results of the lithium ion secondary batteries of Examples 1 to 16, 19 to 23, Reference Examples 17 to 18 and Comparative Examples 1 to 2.
Further, FIG. 1 shows fluctuations in the integrated irreversible capacity value during the cycle test in Example 1 and Comparative Example 1. The curve shown in FIG. 1 is a cumulative irreversible capacity value fluctuation curve with the vertical axis representing the total irreversible capacity [mAh / g] and the horizontal axis representing the number of cycles. In FIG. 1, the solid line represents the total irreversible capacity value fluctuation during the cycle test of Example 1, and the dotted line represents the total irreversible capacity value fluctuation during the cycle test of Comparative Example 1.
Table 1 shows whether or not the positive electrode active material particles are coated with inorganic phosphate particles in the “Presence or absence of inorganic phosphate particles” column. A case where the positive electrode active material particles are coated with inorganic phosphate particles is indicated as “present”.

From the results in Table 1, when comparing Examples 1 to 12 and Comparative Examples 1 and 2, the lithium ion secondary batteries of Examples 1 to 12 to which inorganic phosphate particles were added were obtained by using inorganic phosphate particles. Compared to the lithium ion secondary batteries of Comparative Examples 1 and 2 that were not added, the negative electrode Fe amount was reduced, the integrated irreversible capacity was reduced, and the capacity retention rate was confirmed to be 60% or more. It was.
Further, when Examples 1 and 2 are compared with Examples 13 to 16, the amount of negative electrode Fe tends to decrease as the mass ratio (inorganic phosphate particles / positive electrode active material particles) increases, and the integrated irreversible capacity While the tendency to decrease was confirmed, the tendency to decrease the discharge capacity was also confirmed. The discharge capacity is lowered because the electron conductivity of the positive electrode mixture layer is excessively impaired due to an excessive increase in the proportion of inorganic phosphate particles having low electron conductivity. It is considered that two factors are that the capacity is simply lowered because there is no electrochemical activity.

Also, as in Example 1, comparing the reference examples 17 and 18, in Reference Examples 17 and 18 the positive electrode active material particle inorganic phosphate on the surface has the form of coated, many negative Fe content, positive Thus, it can be seen that the effect of suppressing the elution of the transition metal is not sufficiently exhibited.

  In addition, when Examples 19 to 23 and Comparative Example 1 are compared, the amount of negative electrode Fe can be reduced even when inorganic phosphate particles are mixed during preparation of the positive electrode material paste, and the inorganic phosphate particles are between the positive electrode and the separator. Even if a layer is formed, the amount of negative electrode Fe can be reduced, the amount of negative electrode Fe can be reduced by mixing inorganic phosphate particles in the electrolyte, and the amount of negative electrode Fe can be reduced even if inorganic phosphate particles are supported on the separator. It can be seen that even if inorganic phosphate particles are mixed during preparation of the negative electrode material paste, the amount of negative electrode Fe is reduced. If the inorganic phosphate particles can be placed where the transition metal ions eluted from the positive electrode can pass, the amount of transition metal eluted from the positive electrode reaches the negative electrode regardless of the location of the inorganic phosphate particles. It is thought that it can be reduced.

  Further, from the results of FIG. 1, the lithium ion secondary battery of Example 1 shows no tendency to increase except for the irreversible capacity increased at the beginning of the cycle, suggesting that Fe elution from the positive electrode is small. Although it turns out that it is excellent in the characteristic as an ion secondary battery, the lithium ion secondary battery of the comparative example 1 has always produced the irreversible capacity | capacitance during a cycle, and suggests that there is much Fe elution from a positive electrode, It turns out that the characteristic as an ion secondary battery is inferior compared with Example 1. FIG.

  The lithium ion secondary battery of the present invention can suppress the elution of transition metals from the positive electrode, so it has excellent long-term cycle characteristics, and can improve stability and safety. Can greatly contribute to the advancement of the reliability of lithium ion secondary batteries.

Claims (5)

A lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte,
Contains inorganic phosphate (except lithium aluminum titanium phosphate) particles,
The positive electrode is LixAyMzPO ₄ (0 ≦ x ≦ 1.1, 0.8 ≦ y ≦ 1.1, 0 ≦ z ≦ 0.2, where A is selected from the group consisting of Fe, Mn, Co, and Ni M is at least one selected from the group consisting of Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and rare earth elements) And a positive electrode active material particle having a carbonaceous film covering the surface of the central particle. The positive electrode is composed of composite particles in which the positive electrode active material particle is attached to the surface of the inorganic phosphate particle. The
The inorganic phosphate particles include a base metal, a semimetal, or a transition metal, and have a transition metal / phosphorus ratio (substance ratio) of 0.5 or less . The inorganic phosphate particles contain at least one selected from the group consisting of alkali metals and alkaline earth metals, in claim 1 the transition metal / phosphorus ratio (amount of substance ratio) is 0.5 or less The lithium ion secondary battery as described. A lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte,
Contains inorganic phosphate (except lithium aluminum titanium phosphate) particles,
The positive electrode is LixAyMzPO ₄ (0 ≦ x ≦ 1.1, 0.8 ≦ y ≦ 1.1, 0 ≦ z ≦ 0.2, where A is selected from the group consisting of Fe, Mn, Co, and Ni M is at least one selected from the group consisting of Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and rare earth elements) Positive electrode active material particles having a center particle and a carbonaceous film covering the surface of the center particle,
The inorganic phosphate particles are represented by LiαPβOγ (0 <α ≦ 3, 0 <β ≦ 2, 0 <γ ≦ 4, 0.5 ≦ α / β ≦ 3.5) ,
The positive electrode is a lithium ion secondary battery comprising composite particles in which the positive electrode active material particles are attached to the surface of the inorganic phosphate particles. A lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte,
Contains inorganic phosphate (except lithium aluminum titanium phosphate) particles,
The positive electrode is LixAyMzPO4 (0 ≦ x ≦ 1.1, 0.8 ≦ y ≦ 1.1, 0 ≦ z ≦ 0.2, where A is selected from the group consisting of Fe, Mn, Co, and Ni. And at least one selected from the group consisting of Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and rare earth elements) A lithium ion secondary battery comprising positive electrode active material particles having a central particle and a carbonaceous film covering the surface of the central particle, wherein the electrolyte contains the inorganic phosphate particles. A lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte,
Contains inorganic phosphate (except lithium aluminum titanium phosphate) particles,
The positive electrode is LixAyMzPO4 (0 ≦ x ≦ 1.1, 0.8 ≦ y ≦ 1.1, 0 ≦ z ≦ 0.2, where A is selected from the group consisting of Fe, Mn, Co, and Ni. And at least one selected from the group consisting of Mg, Ca, Co, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, and rare earth elements) A lithium ion secondary battery comprising positive electrode active material particles having a central particle and a carbonaceous film covering a surface of the central particle, wherein the negative electrode contains the inorganic phosphate particles.