JP2002117849A - Manufacture of positive electrode active material and manufacture of nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a positive electrode active material wherein such battery characteristics as a high capacity and a cycle characteristic are realized. SOLUTION: This has a mixing process to mix a raw material for synthesis of the compound expressed in a general formula LixFe1-yMyPO4 (wherein, in the formula, 0.05<=x<=1.2, 0<=y<=0.8, and M is at least one kind among Mn, Cr, Co, Cu, Ni, V, Mo, TI, Zn, Al, Ga, Mg, B or Nb), a milling process wherein a milling is applied to the mixture obtained by the mixing process and a calcination process to calcine the mixture which has been applied of the milling in the milling process, and a carbon material is added in the either process, and after the milling process, a tap density of the raw material for the synthesis is made to be not less than 0.4 g/cc and not more than 2.0 g/cc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a positive electrode active material capable of reversibly doping and undoping lithium and a method for producing a nonaqueous electrolyte battery using the positive electrode active material.

[0002]

2. Description of the Related Art In recent years, along with the remarkable progress of various electronic devices, secondary batteries capable of being repeatedly charged and discharged have been studied as a power source that can be used conveniently and economically for a long time. As typical secondary batteries, lead storage batteries, alkaline storage batteries, non-aqueous electrolyte secondary batteries, and the like are known.

[0003] Among the above secondary batteries, a lithium ion secondary battery, which is a nonaqueous electrolyte secondary battery, has advantages such as high output and high energy density.

[0004] A lithium ion secondary battery is composed of a positive electrode and a negative electrode having an active material capable of reversibly inserting and removing lithium ions, and a non-aqueous electrolyte. Deintercalation occurs in the electrolytic solution, and progresses in the negative electrode by intercalation of lithium ions in the negative electrode active material. On the contrary, when discharging is performed, the above-described reverse reaction proceeds, and lithium ions are intercalated in the positive electrode. That is, charge and discharge can be repeated by repeating a reaction in which lithium ions from the positive electrode enter and exit the negative electrode active material.

At present, as a positive electrode active material of a lithium ion secondary battery, LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are used because of their high energy density and high battery voltage.
Etc. are used.

However, since these positive electrode active materials have a metal element having a low Clark number in their composition, there are problems that the cost is high and stable supply is difficult.
In addition, since these positive electrode active materials have relatively high toxicity and a large effect on the environment, a new positive electrode active material to replace them is required.

On the other hand, LiF having an olivine structure
It has been proposed to use ePO ₄ as a positive electrode active material of a lithium ion secondary battery. LiFePO ₄ has a large volume density of 3.6 g / cm ³ , generates a high potential of 3.4 V, and has a large theoretical capacity of 170 mAh / g. Also,
LiFePO ₄ is a promising material as a positive electrode active material of a lithium ion battery because it contains Li, which can be electrochemically dedoped, per Fe atom in the initial state. In addition, LiFePO ₄ has iron in its composition, which is an inexpensive material that is abundant and inexpensive, and is therefore lower in cost than the above-mentioned LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , and The effect on the environment is small due to its low toxicity.

However, since the electronic conductivity of LiFePO ₄ is low, when LiFePO ₄ is used as the positive electrode active material, the internal resistance of the battery may increase. As a result, there is a problem that the polarization potential at the time of the closed circuit of the battery increases due to the increase in the internal resistance of the battery, and the battery capacity decreases. Moreover, since the true density of LiFePO ₄ is lower than that of the conventional cathode material amount, the case of using LiFePO ₄ as the positive electrode active material, it is impossible to increase the active material packing ratio sufficiently, the energy density of the battery well There is a problem that can not be increased.

[0009]

SUMMARY OF THE INVENTION Therefore, LiFePO
_{As a} positive electrode active material having better electron conductivity than _4, it has an olivine structure and has a general formula Li _x FePO ₄ (where
≦ x ≦ 1. It has been proposed to use a composite of a compound represented by the formula (1) and a carbon material (hereinafter, referred to as a LiFePO ₄ carbon composite).

Incidentally, in order to improve battery characteristics, it is necessary to manufacture a non-aqueous electrolyte secondary battery using a positive electrode active material containing no impurities.

As a method for producing the Li _x FePO ₄ carbon composite having the olivine structure, which is used as a positive electrode active material, a raw material of Li _x FePO ₄ is mixed, fired at a predetermined temperature, and At this point, a method of adding a carbon material has been proposed.

However, since it is difficult to smoothly progress the synthesis reaction for synthesizing Li _x FePO ₄ by sintering the synthesis raw materials in the firing step, a single-phase synthesis of the Li _x FePO ₄ carbon composite is realized. It is not at present.

[0013] That is, a technique for reliably synthesizing the Li _x FePO ₄ carbon composite in a single phase has not been established, and a nonaqueous electrolyte secondary battery using the Li _x FePO ₄ carbon composite synthesized in a single phase has also been realized. Not.

The present invention has been proposed in view of such a conventional situation, and has been proposed in which the Li _x FePO ₄ carbon composite and a part of Fe of the Li _x FePO ₄ carbon composite are substituted with another metal element. Carbon composite, that is, Li _x Fe _1-y
M _y PO ₄ carbon composite material (wherein, 0.05 ≦ x ≦ 1.
2, 0 ≦ y ≦ 0.8, and M is Mn, Cr, Co, C
u, Ni, V, Mo, TI, Zn, Al, Ga, Mg,
At least one of B and Nb. ), And to provide a method for producing a positive electrode active material that realizes excellent battery characteristics. Further, by using this way _{Li x Fe 1-y M y} PO 4 carbon composite material which is manufactured as a positive electrode active material, a manufacturing method of the nonaqueous electrolyte battery having excellent battery characteristics such as battery capacity and cycle characteristics The purpose is to do.

[0015]

In order to achieve the above-mentioned object, a method for producing a positive electrode active material according to the present invention has a general formula L
_{i x Fe 1-y M y} PO 4 ( In the formula, 0.05 ≦ x ≦ 1.
2, 0 ≦ y ≦ 0.8, and M is Mn, Cr, Co, C
u, Ni, V, Mo, TI, Zn, Al, Ga, Mg,
At least one of B and Nb. A) a mixing step of mixing the synthetic raw materials of the compound represented by the above, a milling step of milling the mixture obtained in the mixing step, and a firing step of firing the mixture milled in the milling step, Further, a carbon material is added in any of the above steps, and after the milling step, the tap density of the synthetic raw material is set to 0.4 g / cc or more and 2.0 g / cc or less.

According to the method for producing a positive electrode active material according to the present invention through the above steps, the tap density of the synthesis raw material after the milling step is defined as described above, so that the synthesis raw material is sufficiently miniaturized. Thus, the contact area where the synthetic raw materials contact each other in the firing step is sufficiently ensured. Therefore, according to this method for producing a positive electrode active material, the reaction efficiency of the synthesis reaction in the firing step is good, and the single-phase synthesized Li _x
Complex with Fe _1-y M _y PO ₄ carbon material, that is, the positive electrode active material in which no impurity is contained is produced. Note that milling refers to simultaneous grinding and mixing.

Further, a method of manufacturing a nonaqueous electrolyte battery according to the present invention is a method of manufacturing a nonaqueous electrolyte battery including a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a nonaqueous electrolyte. When producing the positive electrode active material, a general formula Li _x Fe _{1- y My} PO ₄ (where 0.05 ≦ x ≦
1.2, 0 ≦ y ≦ 0.8, and M is Mn, Cr, C
o, Cu, Ni, V, Mo, TI, Zn, Al, Ga,
At least one of Mg, B, and Nb. A) a mixing step of mixing the synthetic raw materials of the compound represented by the above, a milling step of milling the mixture obtained in the mixing step, and a firing step of firing the mixture milled in the milling step. In addition, a carbon material is added in any of the above steps, and after the above-mentioned milling step, the tap density of the synthetic raw material is set to 0.4 g / cc or more,
cc or less.

According to the method of manufacturing a nonaqueous electrolyte battery according to the present invention through the above steps, Li _x F
Since complex with e _1-y M _y PO ₄ and the carbon material can be reliably single-phase synthesis, a non-aqueous electrolyte battery excellent in battery characteristics such as battery capacity and cycle characteristics can be manufactured.

[0019]

Embodiments of the present invention will be described below.

As shown in FIG. 1, a non-aqueous electrolyte battery 1 manufactured by applying the present invention contains a negative electrode 2, a negative electrode can 3 containing the negative electrode 2, a positive electrode 4, and a positive electrode 4. Positive electrode can 5
And a separator 6 disposed between the positive electrode 4 and the negative electrode 2,
An insulating gasket 7 is provided, and the negative electrode can 3 and the positive electrode can 5 are filled with a non-aqueous electrolyte.

The negative electrode 2 is made of, for example, a metal lithium foil serving as a negative electrode active material. When a material that can be doped and dedoped with lithium is used as the negative electrode active material, the negative electrode 2 is formed by forming a negative electrode active material layer containing the negative electrode active material on a negative electrode current collector. As the negative electrode current collector, for example, a nickel foil or the like is used.

As the negative electrode active material capable of doping and undoping lithium, lithium metal, a lithium alloy, a conductive polymer doped with lithium, a layered compound such as a carbon material and a metal oxide can be used.

As the binder contained in the negative electrode active material layer, a known resin material or the like which is generally used as a binder for the negative electrode active material layer in this type of nonaqueous electrolyte battery can be used.

The negative electrode can 3 houses the negative electrode 2 and serves as an external negative electrode of the nonaqueous electrolyte battery 1.

The positive electrode 4 contains a positive electrode active material capable of electrochemically releasing lithium and reversibly occluding lithium on a positive electrode current collector made of, for example, an aluminum foil. The positive electrode active material layer is formed.

As the positive electrode active material, Li_xFe_1-yM_yP
O_FourAnd a composite of a carbon material. This complex is described in detail
Although the detailed manufacturing method will be described later, it has an olivine structure,
Formula Li _xFe_1-yM_yPO_Four(However, in the formula, 0.05 ≦ x ≦
1.2, 0 ≦ y ≦ 0.8, and M is Mn, Cr, C
o, Cu, Ni, V, Mo, TI, Zn, Al, Ga,
At least one of Mg, B, and Nb. )so
A mixing step of mixing the synthetic raw materials of the represented compound, and
Millin milling the mixture obtained in the mixing step
And the mixture milled in the above milling step
And a firing step of firing
It is manufactured by adding a carbon material.

Hereinafter, LiF is referred to as Li _x Fe _{1- y My} PO _4.
A case in which ePO ₄ is synthesized and a composite composed of ePO ₄ and a carbon material (hereinafter, referred to as a LiFePO ₄ carbon composite) is used as a positive electrode active material will be described. Note that the present invention is not limited to this.

LiFePO_FourThe carbon composite is LiFeP
O_FourThe surface of the particles has the LiFePO _FourCompared to particle size
Particles of carbon material with a very small particle size
Individually attached. Carbon material has conductivity
Therefore, carbon material and LiFePO_FourL composed of
iFePO_FourThe carbon composite is, for example, LiFePO_FourCompare with
Then, the electron conductivity is excellent. That is, LiFeP
O_FourThe carbon composite is LiFePO_FourAttached to the surface of the particles
Since the electron conductivity is improved by the carbon particles, LiF
ePO_FourThe original capacity is fully drawn out. Accordingly
As a positive electrode active material, LiFePO_FourUsing carbon composite
To achieve high capacity non-aqueous electrolyte battery 1
it can.

The carbon content per unit weight of the LiFePO ₄ carbon composite is preferably at least 3% by weight. If the carbon content per unit weight in the LiFePO ₄ carbon composite is less than 3% by weight, LiFe
Since the amount of carbon particles adhering to the surface of the PO ₄ particles is not sufficient, the effect of improving the electron conductivity may not be sufficiently obtained.

As a carbon material constituting the LiFePO ₄ carbon composite, a Raman spectrum of graphite (hereinafter referred to as Gr) has a Raman spectrum of 1 in Raman spectroscopy.
Those having an intensity area ratio A (D / G) of a diffraction line appearing at a wave number of 1570 to 1590 cm ^-1 with respect to a diffraction line appearing at 340 to 1360 cm ^-1 of 0.3 or more can be suitably used.

Here, the intensity area ratio A (D / G) is shown in FIG.
The wave number 157 measured by Raman spectroscopy as shown in FIG.
G peak and wave number 1340 appearing at ⁰ to 1590 cm ^-1
Raman spectrum intensity area ratio A (D / G) not including background with D peak appearing at ~ 1360 cm ^-1
Is defined. Further, not including the background means not including a noise portion.

[0032] As described above, two peaks called number is D peak appearing at G peak and the wave number 1340～1360Cm ^-1 appearing at wave number 1570～1590Cm ^-1 in the peak of the Raman spectrum of Gr is observed. Among them, the D peak is not a peak originally derived from the G peak but a Raman inactive peak that appears when the structure is distorted and the symmetry of the structure is reduced. Therefore, the D peak is
It is a measure of the distorted structure of Gr, and it is known that the intensity area A (D / G) of the D peak and the G peak has a linear relationship with the reciprocal of the crystallite size La in the a-axis direction of Gr.

As such a carbon material, specifically, an amorphous carbon material such as acetylene black can be preferably used.

Further, the intensity area ratio A (D / D
The carbon material having G) of 0.3 or more can be obtained by performing a treatment such as crushing with a crusher. Then, by controlling the pulverization time, any A
A carbon material having (D / G) can be obtained.

For example, graphite, which is a crystalline carbon material, is crushed using a powerful crusher such as a planetary ball mill, so that its structure is easily broken and amorphousization proceeds. (D / G) increases. That is, by controlling the operation time of the pulverizer, an arbitrary A (D / D /
G), that is, a carbon material of 0.3 or more can be easily obtained. Therefore, by pulverizing, a crystalline carbon-based material or the like can be preferably used as the carbon material.

The powder density of the LiFePO ₄ carbon composite is preferably 2.2 g / cm ³ or more. L
The powder density of the iFePO ₄ carbon composite is 2.2 g /
When milling is performed on the synthetic raw material to an extent of not less than cm ^{3, the} raw material becomes sufficiently miniaturized. Therefore, the filling rate of the positive electrode active material is improved, and the nonaqueous electrolyte battery 1 having a high capacity can be realized. Further, since the LiFePO ₄ carbon composite is miniaturized so as to satisfy the powder density, it can be said that the specific surface area of LiFePO ₄ is also increased. That is, the contact area between LiFePO ₄ and the carbon material can be sufficiently secured, and the electron conductivity can be improved.

[0037] If the powder density of the LiFePO ₄ carbon composite material is less than 2.2 g / cm ^3, since the LiFePO ₄ carbon composite material is not compressed sufficiently, can not be improved active material filling rate of the positive electrode 4 There is a fear.

The LiFePO ₄ carbon composite preferably has a Brunauer-Emmett-Teller (hereinafter referred to as BET) specific surface area of 10.3 m ² / g or more.
The BET specific surface area of the LiFePO ₄ carbon composite is 10.3
m ² / g or more, LiF per unit weight
The specific surface area of ePO ₄ can be made sufficiently large, and the contact area between LiFePO ₄ and the carbon material can be increased. Therefore, the electron conductivity of the positive electrode active material can be reliably improved.

Further, the primary particle size of the LiFePO ₄ carbon composite is preferably not more than 3.1 μm. LiF
By setting the primary particle size of the ePO ₄ carbon composite to 3.1 μm or less, the specific surface area of LiFePO ₄ per unit weight can be made sufficiently large, and LiF
The contact area between ePO ₄ and the carbon material can be increased. Therefore, the electron conductivity of the positive electrode active material can be reliably improved.

As the binder contained in the positive electrode active material layer, a known resin material or the like which is generally used as a binder for the positive electrode active material layer in this type of nonaqueous electrolyte battery can be used.

The positive electrode can 5 accommodates the positive electrode 4 and serves as an external positive electrode of the nonaqueous electrolyte battery 1.

The separator 6 separates the positive electrode 4 and the negative electrode 2 from each other. For example, a known material which is generally used as a separator for this type of non-aqueous electrolyte battery can be used. A polymer film is used. Also, from the relationship between lithium ion conductivity and energy density, it is necessary that the thickness of the separator be as small as possible. Specifically, the thickness of the separator is suitably, for example, 50 μm or less.

The insulating gasket 7 is incorporated in the negative electrode can 3 and integrated. The insulating gasket 7 is for preventing the leakage of the nonaqueous electrolyte filled in the negative electrode can 3 and the positive electrode can 5.

As the non-aqueous electrolyte, a solution in which an electrolyte is dissolved in an aprotic non-aqueous solvent is used.

Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyl lactone, sulfolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 2-methyltetrahydrofuran, -Methyl-1,3-dioxolane, methyl propionate, methyl butyrate, dimethyl carbonate, diethyl carbonate,
Dipropyl carbonate and the like can be used. In particular, from the viewpoint of voltage stability, propylene carbonate,
It is preferable to use cyclic carbonates such as ethylene carbonate, butylene carbonate, and vinylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, and dipropyl carbonate. In addition, such a non-aqueous solvent may be used alone or as a mixture of two or more.

As an electrolyte dissolved in a non-aqueous solvent,
Is, for example, LiPF₆, LiClO_Four, LiAsF₆,
LiBF_Four, LiCF_ThreeSO_Three, LiN (CF_ThreeSO_Two)_Twoetc
Can be used. These lithu
LiPF ₆, LiBF_FourUse
Is preferred.

Although the non-aqueous electrolyte battery 1 using a non-aqueous electrolyte has been described as an example of the non-aqueous electrolyte battery to which the present invention is applied, the present invention is not limited to this. The present invention is also applicable when a solid electrolyte is used as the non-aqueous electrolyte. Here, as the solid electrolyte, any of a solid polymer electrolyte such as an inorganic solid electrolyte and a gel electrolyte can be used as long as the material has lithium ion conductivity. Here, examples of the inorganic solid electrolyte include lithium nitride and lithium iodide. The solid polymer electrolyte is composed of an electrolyte salt and a polymer compound that dissolves the electrolyte salt. The polymer compound is a poly (ethylene oxide), an ether polymer such as a crosslinked product thereof, or a poly (methacrylate) ester. A polymer, an acrylate-based polymer, or the like can be used alone, or copolymerized or mixed in the molecule. In this case, as the matrix of the gel electrolyte, for example, various polymer materials can be used as long as they absorb the non-aqueous electrolyte and gel. Examples of such a polymer material include poly (vinylidene fluoride) and poly (vinylidene fluoride).
Fluorine-based polymers such as CO-hexafluoropropylene), poly (ethylene oxide), ether-based polymers such as crosslinked products thereof, and poly (acrylonitrile) can be used. In particular, among these, it is preferable to use a fluoropolymer from the viewpoint of oxidation-reduction stability.

The non-aqueous electrolyte battery 1 configured as described above
The manufacturing method of the will be described below.

First, a composite of Li _x FePO ₄ as a positive electrode active material and a carbon material is synthesized according to the following production method.

To synthesize this positive electrode active material, Li _x F
The raw materials for ePO ₄ are mixed, milled, fired, and a carbon material is added at any of the above points. L
The starting materials for synthesis of i _x FePO _4, and Li ₃ PO _4, Fe
₃ (PO ₄ ) ₂ or its hydrate, Fe ₃ (PO ₄ ) ₂ .n
H ₂ O (where n is the hydration number) is used.

Hereinafter, lithium phosphate (Li ₃ PO ₄ ) and ferrous phosphate octahydrate (Fe ₃ (PO ₄ ) ₂ .8H ₂ O) synthesized as described below are used as synthesis raw materials. ) To synthesize a LiFePO ₄ carbon composite by performing various steps after adding a carbon material to this synthesis raw material.

First, a mixing step of mixing a raw material of LiFePO ₄ and a carbon material to form a mixture is performed. Then
A milling step of milling the mixture obtained in the mixing step is performed. Next, a firing step of firing the mixture milled in the milling step is performed.

In the mixing step, lithium phosphate and ferrous phosphate octahydrate are mixed at a predetermined ratio as a raw material for synthesis, and a carbon material is further added to form a mixture.

[0054] iron phosphate I octahydrate be used as raw material for the synthesis, iron sulfate heptahydrate and (FeSO ₄ · 7H ₂ O) in an aqueous solution comprising dissolved in water, sodium hydrogen phosphate two hundred twelve hydration A product (2Na ₂ HPO ₄ .12H ₂ O) is added and left for a predetermined time to synthesize. The synthesis reaction of ferrous phosphate octahydrate is represented by the following reaction formula 1.

[0055]

Embedded image

For ferrous phosphate octahydrate, which is a raw material for synthesis,
Has a certain amount of Fe in the synthesis process. ³⁺Contains
You. Fe for synthetic material³⁺Is remaining, the trivalent
Since an Fe compound is generated, LiFePO_FourCarbon composite
The single-phase synthesis of the body is hindered. Therefore, before firing
A reducing agent is added to the raw material for synthesis, and contained in the raw material for synthesis during firing.
Fe³⁺Is Fe²⁺Need to be reduced to

However, the ability of the reducing agent to reduce Fe ³⁺ to Fe ²⁺ is limited. If the content of Fe ^{3+ in} the raw material for synthesis is too high, the Fe ³⁺ cannot be completely reduced and LiFeP
It may remain in the O ₄ carbon composite.

Therefore, the content of Fe ³⁺ with respect to the total amount of iron in ferrous phosphate octahydrate is preferably not more than 61% by weight. By preliminarily limiting the content of Fe ^{3+ to} the total amount of iron in ferrous phosphate octahydrate, which is a synthetic raw material, to 61% by weight or less, Fe ³⁺ does not remain during firing, The single-phase synthesis of the LiFePO ₄ carbon composite can be reliably performed without generating impurities due to ³⁺ .

It should be noted that the longer the standing time when ferrous phosphate octahydrate is formed, the higher the content of Fe ^{3+ in} the product becomes. Thus, ferrous phosphate octahydrate having an arbitrary Fe ³⁺ content can be produced. The content of Fe ³⁺ with respect to the total amount of iron in ferrous phosphate octahydrate can be measured by the Mossbauer measurement method.

The carbon material added to the synthesis raw material is
Fe contained in ferrous phosphate octahydrate as a raw material for synthesis²⁺But
Fe or oxygen in the atmosphere³⁺As oxidized to
Also, when firing³⁺Is Fe²⁺Acts as a reducing agent to reduce
Good. Therefore, Fe³⁺And that
However, generation of impurities is prevented, and LiFePO_FourCarbon compound
A single-phase synthesis of the coalescing becomes possible. In addition, carbon materials
Fe contained in raw materials ²⁺Fe³⁺Acid to prevent oxidation to
Works as an antioxidant. In other words, the carbon material is
Is the amount of oxygen present in the atmosphere and in the furnace during firing.
From Fe²⁺Is Fe³⁺To prevent oxidation to
You.

That is, the carbon material functions as a conductive agent for improving the electron conductivity of the positive electrode active material as described above, and also functions as a reducing agent and an antioxidant. Incidentally, since this carbon material is a component of the LiFePO ₄ carbon composite material, there is no need to remove after the synthesis of the LiFePO ₄ carbon composite material. Therefore, the production of the LiFePO ₄ carbon composite is made more efficient.

The carbon content per unit weight of the LiFePO ₄ carbon composite is preferably at least 3% by weight. By setting the carbon content per unit weight of the LiFePO ₄ carbon composite to 3% by weight or more, LiFePO ₄
It is possible to sufficiently draw out the capacity and cycle characteristics that PO ₄ originally has.

In the milling step, the mixture obtained in the mixing step is subjected to milling that is simultaneously performed with pulverization and mixing. Milling in the present invention means powerful grinding and mixing using a ball mill. As the ball mill, for example, a planetary ball mill, a shaker type ball mill, a mechanofusion, and the like can be suitably used.

By subjecting the mixture obtained in the mixing step to milling, the raw materials for synthesis and the carbon material can be uniformly mixed. Further, when the synthesis raw material is refined by milling, the specific surface area of the synthesis raw material can be increased. Therefore, the contact points between the raw materials increase,
The synthesis reaction in the subsequent baking step can proceed promptly.

In the present invention, the mixture containing the raw material for synthesis
Milling is performed to increase the tap density of the synthetic raw material to 0.4 g /
cc or more and 2.0 g / cc or less. Especially milling
The tap density of the synthetic raw material after the process is 0.6 g / cc or more,
It is preferred to be 2.0 g / cc or less. After milling
The tap density of the synthetic raw material is specified as described above.
The raw materials for synthesis are sufficiently fine,
To ensure a sufficient contact area between the synthetic raw materials
be able to. Therefore, a method for producing this positive electrode active material
According to the above, the reaction efficiency of the synthesis reaction in the firing step is good.
LiFePO _FourEnsure single-phase synthesis of carbon composites
be able to. As a result, high capacity and cycle characteristics
An excellent non-aqueous electrolyte secondary battery 1 can be realized.

By milling, the tap density was 0.4 g /
When the synthetic raw material is less than cc, the synthetic raw material is not sufficiently refined, and the specific surface area is small. For this reason, the contact area between the raw materials becomes insufficient, and the reaction efficiency of the synthesis reaction in the subsequent baking step deteriorates. Also, tap density is 2.0g / cc by milling.
When the synthesis raw material exceeds the above, the synthesis reaction in the subsequent firing step excessively proceeds, and LiFePO ₄ particles grow excessively. As a result, the specific surface area of LiFePO ₄ is small, and the contact area with the carbon material is small, so that the positive electrode active material has deteriorated electron conductivity.

Further, it is preferable that the particle size distribution of the particles having a particle diameter of 3 μm or more is reduced to 22% or less as a volume-based integration frequency by milling. Assuming that the particle size distribution of the synthetic raw material is within the above range, the synthetic raw material has a surface area that is large enough to obtain sufficient surface activity for the synthesis reaction. Therefore, even if the firing temperature is as low as the melting point of the synthesis raw material, for example, 600 ° C., the reaction efficiency is good, and the single-phase synthesis of the LiFePO ₄ carbon composite can be reliably performed.

Further, milling is preferably performed so that the powder density of the LiFePO ₄ carbon composite becomes 2.2 g / cm ³ or more. The specific surface area of LiFePO ₄ can be increased by miniaturizing the synthesis raw material so as to have the above powder density. Thereby, LiFe
The contact area between PO ₄ and the carbon material can be increased, and the electron conductivity of the positive electrode active material can be improved. Therefore, by milling the mixture containing the raw materials for synthesis, it is possible to manufacture a positive electrode active material that realizes the nonaqueous electrolyte battery 1 having a high capacity.

In the firing step, the mixture milled in the milling step is fired. By firing the mixture, lithium phosphate and ferrous phosphate octahydrate are reacted to synthesize LiFePO ₄ .

The synthesis reaction of LiFePO ₄ is represented by the following reaction formula 2. In the reaction formula shown below, Li ₃ PO ₄ and Fe ₃ (PO ₄ ) ₂ or its hydrate Fe ₃ (PO ₄ ) ₂ .nH ₂ O (where n is the hydration number) ) Is shown.

[0071]

Embedded image

As is apparent from the reaction formula shown in Chemical formula 2, no by-product is produced when Fe ₃ (PO ₄ ) ₂ is used as a raw material for synthesis. When Fe ₃ (PO ₄ ) ₂ .nH ₂ O is used, only non-toxic water is generated as a by-product, but the amount of the by-product is small. Therefore, LiF
The yield of ePO ₄ can be greatly improved.

The firing temperature at the time of firing the mixture can be set at 400 ° C. to 900 ° C. by the above-described synthesis method, but is preferably about 600 ° C. in consideration of battery performance. When the calcination temperature is lower than 400 ° C., the chemical reaction and crystallization do not proceed sufficiently, and the raw material Li
There is a possibility that an impurity phase such as ₃ PO ₄ exists and uniform LiFePO ₄ cannot be obtained. If conversely the sintering temperature exceeds 900 ° C., the particles of the LiFePO ₄ crystallization progresses excessively increases, decreases the contact area between LiFePO ₄ and the carbon material to render decreases, sufficient discharge There is a possibility that the capacity cannot be obtained.

At the time of firing, the synthesized LiFePO
Fe in the _four- carbon composite is in a divalent state. For this reason,
At a synthesis temperature of about 600 ° C., LiF
Fe in the ePO ₄ carbon composite is immediately oxidized to Fe ³⁺ by oxygen in the firing atmosphere according to a reaction formula shown in the following chemical formula (3). As a result, impurities such as a trivalent Fe compound are generated, and the single-phase synthesis of the LiFePO ₄ carbon composite is hindered.

[0075]

Embedded image

Therefore, nitrogen and argon are used as the firing atmosphere.
Etc. or a reducing gas such as hydrogen or carbon monoxide.
And the oxygen concentration in the firing atmosphere was adjusted to LiFe
PO _FourThe range where Fe in the carbon composite is not oxidized, that is,
More preferably, it is 1012 ppm by volume or less. Firing
Reduce the oxygen concentration in the atmosphere to 1012 vol ppm or less
Thus, even at a synthesis temperature of about 600 ° C.,
Oxidation prevention, LiFePO_FourSingle phase synthesis of carbon composites
It can be performed reliably.

The oxygen concentration in the firing atmosphere is 1012 volume p
When the pressure is higher than pm, the amount of oxygen in the firing atmosphere is too large, so that Fe in the LiFePO ₄ carbon composite is Fe ³⁺
This may cause oxidation of the LiFePO ₄ carbon composite, which may hinder single-phase synthesis of the LiFePO ₄ carbon composite.

[0078] For removal of the sintered LiFePO ₄ carbon composite material is taken out temperature of the sintered LiFePO ₄ carbon composite material, that is, the temperature of the LiFePO ₄ carbon composite material when exposed to atmosphere, the LiFePO ₄ carbon composite material is The temperature is preferably 305 ° C. or lower. In addition, L after firing
More preferably, the temperature for taking out the iFePO ₄ carbon composite is 204 ° C. or lower. By setting the temperature at which the LiFePO ₄ carbon composite is taken out to 305 ° C. or lower, it is possible to prevent the Fe in the fired LiFePO ₄ carbon composite from being oxidized by oxygen in the atmosphere and generating impurities.

[0079] When taken out in an insufficiently cooled state of the LiFePO ₄ carbon composite material after sintering, LiFePO ₄ Fe of carbon composite material is oxidized by oxygen in the atmosphere, there is a fear that impurities are generated. However, if the LiFePO ₄ carbon composite is cooled to an extremely low temperature, there is a possibility that the working efficiency may be reduced.

Therefore, by setting the temperature at which the calcined LiFePO ₄ carbon composite is taken out to 305 ° C. or lower, Fe in the calcined LiFePO ₄ carbon composite is oxidized by oxygen in the atmosphere to generate impurities. LiFePO 4 having favorable characteristics as battery characteristics, while maintaining the work efficiency.
_{A four-} carbon composite can be efficiently synthesized.

The LiFePO ₄ carbon composite after firing is cooled in a firing furnace, and the cooling method at this time may be natural cooling or forced cooling. However, in consideration of shortening the cooling time, that is, considering the working efficiency, it is preferable to perform forced cooling. Then, in the case of forced cooling, the inside of the firing furnace has the above-described oxygen concentration, that is, 1%.
What is necessary is just to supply a mixed gas of oxygen and an inert gas or only an inert gas into the firing furnace so as to be 012 vol ppm or less.

In the above description, the addition of the carbon material is performed before the milling step. However, the addition of the carbon material may be performed after the milling step or after the firing step.

However, the carbon material is added after the firing step.
In the case, to obtain the reduction effect and the oxidation prevention effect during firing
Can not be used, it is used only for the effect of improving conductivity
The matter is attached. Therefore, the carbon material is added after the firing step.
In other cases, the Fe ³⁺Can be prevented from remaining
Required.

Further, when the carbon material is added after the firing step,
In this case, the product synthesized by firing is LiFePO_Fourcarbon
LiFePO, not a composite_FourIt is. So firing
Synthesized by LiFePO_FourAdded carbon material to
Then, milling is performed again. By re-milling
The added carbon material is refined, and LiFePO_Fourof
It easily adheres to the surface. Also, do not perform milling again.
And LiFePO _FourAnd carbon material are well mixed
Therefore, the refined carbon material is converted to LiFePO_FourTable
It can be uniformly attached to the surface. Therefore, firing
Even if a carbon material is added later, the milling process
The same product as when carbon material was added before, that is,
LiFePO_FourIt is possible to obtain a carbon composite,
In addition, the same effect as described above can be obtained.

In the above, Li_xFePO_Fourof
Li as synthesis material_ThreePO_FourAnd Fe _Three(PO_Four)_TwoOr that
Fe, a hydrate of_Three(PO_Four)_Two・ NH_TwoO (however, n
Is the hydration number. ) Was used.
However, the present invention is not limited to this, and Li_xFePO_FourSynthesis of
Raw materials: lithium carbonate, ammonium dihydrogen phosphate
And iron (II) acetate are mixed at a predetermined ratio, and calcined,
By the reaction shown in FIG._FourCan also be synthesized
It is possible.

[0086]

Embedded image

The LiFePO ₄ obtained as described above
Non-aqueous electrolyte battery 1 using carbon composite as positive electrode active material 1
Is manufactured, for example, as follows.

For the negative electrode 2, first, a negative electrode active material and a binder are dispersed in a solvent to prepare a negative electrode mixture of a slurry. Next, the obtained negative electrode mixture is uniformly applied on the current collector,
The negative electrode 2 is produced by drying to form a negative electrode active material layer. As the binder of the negative electrode mixture, a known binder can be used, and a known additive or the like can be added to the negative electrode mixture. Further, metallic lithium serving as a negative electrode active material can be used as the negative electrode 2 as it is.

As the positive electrode 4, first, a LiFePO ₄ carbon composite as a positive electrode active material and a binder are dispersed in a solvent to prepare a slurry positive electrode mixture. Next, the obtained positive electrode mixture is uniformly applied on a current collector and dried to form a positive electrode active material layer, whereby the positive electrode 4 is manufactured. Known binders can be used as the binder of the positive electrode mixture, and known additives and the like can be added to the positive electrode mixture.

The non-aqueous electrolyte is prepared by dissolving an electrolyte salt in a non-aqueous solvent.

Then, the negative electrode 2 is accommodated in the negative electrode can 3, the positive electrode 4 is accommodated in the positive electrode can 5, and a separator 6 made of a polypropylene porous film or the like is disposed between the negative electrode 2 and the positive electrode 4. The coin-type nonaqueous electrolyte battery 1 is completed by injecting the nonaqueous electrolyte into the negative electrode can 3 and the positive electrode can 5 and caulking and fixing the negative electrode can 3 and the positive electrode can 5 via the insulating gasket 7. I do.

The LiFePO manufactured as described above
Non-aqueous electrolyte battery 1 using a ₄ carbon composite as a positive electrode active material
The filling rate of the positive electrode active material is high, and the electron conductivity is excellent. Therefore, the non-aqueous electrolyte battery 1 has a large capacity because doping and de-doping of lithium ions is performed well, and the excellent cycle characteristics inherent in LiFePO ₄ are sufficiently brought out. Excellent cycle characteristics.

The shape of the nonaqueous electrolyte battery 1 according to the present embodiment as described above is not particularly limited, such as a cylindrical type, a square type, a coin type, and a button type.
In addition, various sizes such as a thin type and a large size can be used.

[0094]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on specific experimental results.

Example 1 [Preparation of Positive Electrode Active Material] First, Li ₃ PO ₄ and Fe ₃ (P
O ₄₎ and ₂ · 8H ₂ O, the element ratio of lithium and iron is 1: 1 were mixed so that, further a primary particle size of 0.3
μm Ketjen Black was added to make a mixture. Next, the mixture and alumina balls having a diameter of 10 mm were put into a 100 mm diameter alumina pot at a mass ratio of mixture: alumina balls = 1: 2, and the mixture was milled using a planetary ball mill. As a planetary ball mill, an experimental planetary rotary pot mill “LA-PO ₄ ” (manufactured by Ito Seisakusho) was used, and milling was performed under the following conditions.

Planetary ball mill milling conditions Revolution radius: 200 mm Revolution speed: 230 rpm Rotation speed: 230 rpm Operating time: 10 hours Next, the tap density of the mixture that has been milled in the above is shown by the Ishiyama type specific volume shown in FIG. It measured using the test machine.

This tester comprises two metal tubes 13 each containing a test tube with a capacity of 20 ml in a test box 12 having a rubber plate 11 laid on the bottom surface.
Is configured to have a rotary wing 14 for dropping from a predetermined height.

As shown in FIG. 4, the metal tube 13 is a scaled test tube 15 having a capacity of 20 ml (capacity 20 ml, weight 15 to 16 g, height A: 174 to 176 mm, outer diameter B: 16 to 17 mm, (Inner diameter: 14.7 to 15.7 mm)
And is supported in the test box 12 to be vertically movable. The metal tube 13 has a collar 1 at the top.
6 is provided, and its opening is closed by a lid 8. The lid 17 and the collar 16 are connected by a spring 18, and the extension of the spring 18
Is removed, so that the test tube 15 can be taken in and out, and the lid 17 does not come off due to the elastic force of the spring 18 when the metal tube 13 moves up and down.

The rotary blade 14 is disposed between the two metal tubes 13. As shown in FIG. 5, the rotary wing 14 has two key-shaped wings 19 attached at equal intervals, and rotary shafts 20 and 21 penetrating the left and right wall surfaces of the test box 12. At a predetermined height. That is, the rotating blade 14 abuts against the lower surface of the flange 16 of the metal tube 13 when the two blades 19 respectively come to the upper side, and further rotates to lift the flange 16, whereby the metal tube 13 rubber plate 11 at the bottom
Is supported at a position such that the height h from the top is 45 mm.

One rotating shaft 21 supporting the rotating blade 14 is connected to a motor 22 installed outside the test box 12.
And the rotary wings 14 are rotated via the rotary shaft 21 by the driving force of a motor 22. Also, the other one of the rotating shafts 20 supporting the rotor 14
, A counter 23 is attached so that the number of rotations of the rotary blade 14 can be measured.

Therefore, the metal tube 13 is connected to the motor 2
The rotating blade 14 is rotated by 2, and each time the two blades 19 are separated from and brought into contact with the brim portion 16, they are lifted to a position 45 mm higher than the bottom surface, and dropped onto the rubber plate 11 from that position. Then, the number of drops is measured by the counter 23.

The measurement of the tap density of the positive electrode active material is performed using the above-described tester as follows.

First, 5 to 10 g of a precisely weighed sample (for example, 1
0 g) is gently put into a 20-ml test tube 15 with a scale, and the volume at this time (apparent tap density) is read by the scale. Next, the test tube 15 in which the sample is set in this manner is accommodated in the metal tube 13, the lid 17 is closed, and the rotating blades 14 are rotated, so that the metal tube 13 is
A drop operation such as dropping from a position 5 mm higher is performed 400 times, once every two seconds. Thus, the metal tube 13
After dropping, the volume (permanent tap density) of the sample in the test tube 3 is read on a scale.

Then, the tap density is calculated based on the following equation: tap density (g / cc) = sample (g) / volume (cc). This test is performed on four test tubes, and the average value of the results obtained in this test is defined as the tap density of the synthetic raw material after milling. According to this measurement, in Example 1, the tap density of the mixture after milling was 0.40 g / cc.

Next, the mixture after the tap density measurement was put into a ceramic crucible, and placed in an electric furnace in a nitrogen atmosphere at 600 ° C.
At a temperature of 5 hours to obtain a LiFePO ₄ carbon composite as a positive electrode active material.

[Preparation of Test Cell Using Nonaqueous Electrolyte]
A non-aqueous electrolyte battery using the LiFePO ₄ carbon composite obtained as described above as a positive electrode active material was produced.

First, 85 parts by weight of the LiFePO ₄ carbon composite prepared in Example 1 as a positive electrode active material, 10 parts by weight of acetylene black, and 5 parts by weight of poly (vinylidene fluoride) which is a fluororesin powder as a binder Was mixed and then press-formed to obtain a pellet-shaped positive electrode having a diameter of 15.5 mm and a thickness of 0.1 mm.

Next, a negative electrode was obtained by punching out the lithium metal foil in substantially the same shape as the positive electrode.

Then, LiPF ₆ was added to a mixed solvent of propylene carbonate and dimethyl carbonate in an equal volume.
A non-aqueous electrolyte was prepared by dissolving at a concentration of mol / l.

The positive electrode obtained as described above was accommodated in a positive electrode can, the negative electrode was accommodated in a negative electrode can, and a separator was disposed between the positive electrode and the negative electrode. Then, a non-aqueous electrolyte is poured into the positive electrode can and the negative electrode can, and the positive electrode can and the negative electrode can are caulked and fixed.
A coin type test cell of type 16 was produced.

<Example 2> [0111] Except that the revolution speed and the revolution speed of the planetary ball mill were set to 250 rpm,
A LiFePO ₄ carbon composite was produced in the same manner as in Example 1, and a coin-type test cell using this as a positive electrode active material was produced.

<Example 3> [0112] Except that the revolution speed and the revolution speed of the planetary ball mill were set to 270 rpm,
A LiFePO ₄ carbon composite was produced in the same manner as in Example 1, and a coin-type test cell using this as a positive electrode active material was produced.

<Embodiment 4> [0113] Except that the revolution speed and the revolution speed of the planetary ball mill were set to 320 rpm,
A LiFePO ₄ carbon composite was produced in the same manner as in Example 1, and a coin-type test cell using this as a positive electrode active material was produced.

<Comparative Example 1> [0114] Except that the revolution speed and the revolution speed of the planetary ball mill were set to 200 rpm,
A LiFePO ₄ carbon composite was produced in the same manner as in Example 1, and a coin-type test cell using this as a positive electrode active material was produced.

<Comparative Example 2> [0115] Except that the revolution speed and the revolution speed of the planetary ball mill were set to 350 rpm,
A LiFePO ₄ carbon composite was produced in the same manner as in Example 1, and a coin-type test cell using this as a positive electrode active material was produced.

The LiFePO ₄ produced as described above
X-ray diffraction measurement was performed on the carbon composite. And J
CPDS-No. Those which are compatible with the powder X-ray diffraction line described in No. 401499 and for which no other diffraction line is confirmed,
It was evaluated that the single-phase synthesis of the iFePO ₄ carbon composite was performed, and JCPDS-No. Those which did not conform to the powder X-ray diffraction line described in 401499, or were confirmed to have other diffraction lines even if conforming to the above, were evaluated as having no single-phase synthesis of the LiFePO ₄ carbon composite.

Further, in order to evaluate the battery characteristics of the coin-shaped test cell manufactured as described above, a charge / discharge test was performed as described below, and various measurements were performed.

<Charge / Discharge Test> First, for each test cell,
When the battery voltage reaches 4.2 V
Switch from constant current charging to constant voltage charging
The battery was charged while being kept at 4.2 V. And the current
0.01 mA / cm^TwoCharging ends when
I let you. Thereafter, discharge is performed, and the battery voltage is reduced to 2.0 V.
When the discharge is completed, the discharge is terminated, and the
Was measured for the initial discharge capacity. Note that both charging and discharging
At normal temperature (25 ° C.), and the current density at this time is 0.1
mA / cm ^TwoAnd

Next, with the above-mentioned charge / discharge cycle as one cycle, the discharge capacity per weight of the positive electrode active material after 50 cycles was measured. Then, a discharge capacity retention ratio, which is a ratio of the discharge capacity after 50 cycles to the initial discharge capacity, was obtained, and the cycle characteristics were evaluated.

A practical battery is required to have an initial discharge capacity of 140 mAh / g or more and a capacity retention rate of 80% or more. In addition, the initial discharge capacity is 150
mAh / g or more, and the capacity retention ratio is more preferably 90% or more.

Table 1 shows the above measurement results and the measurement results of the tap density.

[0122]

[Table 1]

Table 1 shows that the tap density of the synthetic raw material after milling is 0.4 g / cc or more and 2.0 g / cc in the synthetic raw material of the LiFePO ₄ composite.
The positive electrode active materials of Examples to 4 are JCPDS-No. 401
499, and no other diffraction lines were confirmed, indicating that a single-phase synthesis of the LiFePO ₄ carbon composite was performed. Also, it can be seen that the test cell using this has a large initial discharge capacity and a high capacity retention rate.

On the other hand, in the synthesis raw material of the LiFePO ₄ carbon composite, the cathode active material of Comparative Example 1 in which the tap density of the synthesis raw material after milling is less than 0.4 g / cc is incompatible with the diffraction line. Or, even if it matched, other diffraction lines were confirmed, indicating that the single-phase synthesis of the LiFePO ₄ carbon composite was not performed. In addition, the test cell using this positive electrode active material has a small initial discharge capacity,
It turns out to be impractical.

Further, in the synthesis raw material of the LiFePO ₄ carbon composite, the cathode active material of Comparative Example 2 in which the tap density of the synthesis raw material after milling exceeds 2.0 g / cc is L
Although a single-phase synthesis of the iFePO ₄ carbon composite is being performed, it can be seen that when applied to a test cell, the capacity retention ratio is low, making it impractical.

As described above, when synthesizing the LiFePO ₄ carbon composite, the tap density of the synthesis raw material after milling is set to 0.4 g / cc or more and 2.0 g / cc, whereby the single phase of the LiFePO ₄ carbon composite is It can be said that the positive electrode active material which is synthesized reliably and does not contain impurities can be produced. In addition, it can be said that a non-aqueous electrolyte secondary battery having high capacity and excellent cycle characteristics can be manufactured by using the positive electrode active material manufactured in this manner.

Next, LiFePO 4 was used as the positive electrode active material.
_FourLiFe other than carbon composite_1-yMn _yPO_FourCarbon complex
A plurality of the batteries were synthesized, and the characteristics of batteries using the same were evaluated.

Example 5 LiFe was used as a positive electrode active material.
_A coin-type test cell was produced in the same manner as in Example 1 except that a _0.2 Mn _0.8 PO ₄ carbon composite was synthesized.

Example 6 LiFe was used as a positive electrode active material.
_A coin-type test cell was produced in the same manner as in Example 1 except that a _0.2 Cr _0.8 PO ₄ carbon composite was synthesized.

Example 7 LiFe was used as a positive electrode active material.
_A coin-type test cell was produced in the same manner as in Example 1 except that a _0.2 Co _0.8 PO ₄ carbon composite was synthesized.

Example 8 LiFe was used as a positive electrode active material.
_A coin-type test cell was produced in the same manner as in Example 1 except that a _0.2 Cu _0.8 PO ₄ carbon composite was synthesized.

Example 9 LiFe was used as a positive electrode active material.
_A coin-type test cell was produced in the same manner as in Example 1 except that a _0.2 Ni _0.8 PO ₄ carbon composite was synthesized.

Example 10 LiF was used as the positive electrode active material.
e A coin-type test cell was prepared in the same manner as in Example 1, except that the e _0.25 V _0.75 PO ₄ carbon composite was synthesized.

Example 11 LiF was used as the positive electrode active material.
e A coin-type test cell was produced in the same manner as in Example 1 except that the e _0.25 Mo _0.75 PO ₄ carbon composite was synthesized.

Example 12 LiF was used as the positive electrode active material.
A coin-type test cell was produced in the same manner as in Example 1 except that e _0.25 Ti _0.75 PO ₄ carbon composite was synthesized.

Example 13 LiF was used as the positive electrode active material.
A coin-type test cell was produced in the same manner as in Example 1 except that the e _0.3 Zn _0.7 PO ₄ carbon composite was synthesized.

Example 14 LiF was used as the positive electrode active material.
A coin-type test cell was produced in the same manner as in Example 1, except that e _0.3 Al _0.7 PO ₄ carbon composite was synthesized.

Example 15 LiF was used as the positive electrode active material.
A coin-type test cell was produced in the same manner as in Example 1 except that the e _0.3 Ga _0.7 PO ₄ carbon composite was synthesized.

Example 16 LiF was used as the positive electrode active material.
e A coin-type test cell was produced in the same manner as in Example 1 except that the e _0.25 Mg _0.75 PO ₄ carbon composite was synthesized.

Example 17 LiF was used as the positive electrode active material.
A coin-type test cell was produced in the same manner as in Example 1 except that e _0.25 B _0.75 PO ₄ carbon composite was synthesized.

Example 18 LiF was used as the positive electrode active material.
e A coin-type test cell was produced in the same manner as in Example 1, except that the e _0.25 Nb _0.75 PO ₄ carbon composite was synthesized.

The charge / discharge test described above was similarly performed on the coin-shaped test cells of Examples 5 to 18 manufactured as described above, and the initial discharge capacity and the charge / discharge efficiency were measured. As a result, it was confirmed that the single-phase synthesis of the positive electrode active material was reliably performed in any of the examples, and that the test cell using the same had high capacity and excellent cycle characteristics.

Therefore, as the positive electrode active material, LiFe
_1-y Mn _y upon PO ₄ to synthesize the carbon composite material, the tap density of the starting materials for synthesis after the milling 0.4 g / cc or more, by a 2.0 g / cc, a positive electrode active material in which no impurity is contained It can be said that can be manufactured.
In addition, it can be said that a non-aqueous electrolyte secondary battery having high capacity and excellent cycle characteristics can be manufactured by using the positive electrode active material manufactured in this manner.

[Preparation of Test Cell Using Polymer Electrolyte] <Example 19> First, a gel electrolyte was prepared as follows. First, hexafluoropropylene is used for 6.
A mixture of polyvinylidene fluoride copolymerized at a ratio of 9% by weight, a non-aqueous electrolyte, and dimethyl carbonate,
The mixture was stirred and dissolved to prepare a sol electrolyte solution. Next, vinylene carbonate (V) was added to the sol electrolyte solution.
C) was added at a ratio of 0.5% by weight to obtain a gel electrolyte solution. As a non-aqueous electrolyte, LiPF6 dissolved in a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) at a volume ratio of 6: 4 at a ratio of 0.85 mol / kg. It was used.

Next, a positive electrode was produced as described below. First, 85 parts by weight of the LiFePO ₄ carbon composite prepared in Example 2, 10 parts by weight of acetylene black, and 5 parts by weight of a poly (vinylidene fluoride) which is a fluororesin powder as a binder were mixed. −
A slurry of a positive electrode mixture was prepared by adding methylpyrrolidone. Next, this positive electrode mixture was applied to an aluminum foil having a thickness of 20 μm, heated and dried, and then subjected to a pressing step to produce a positive electrode coated foil. Next, a gel electrolyte solution was applied to one side of the positive electrode coating foil, dried, and the solvent was removed. Then, a 15 mm diameter circle was punched out according to the cell diameter to obtain a positive electrode.

Next, a negative electrode was manufactured as described below. First, a slurry was prepared by mixing 10% by weight of a fluororesin powder as a binder with graphite powder and adding N-methylpyrrolidone. Next, this slurry was applied to a copper foil, heated and dried, and then subjected to a pressing step to punch out a 16.5 mm diameter circle in accordance with the size of the cell to obtain a negative electrode.

The positive electrode obtained as described above is accommodated in a positive electrode can, the negative electrode is accommodated in a negative electrode can, and the positive electrode can and the negative electrode can are caulked and fixed, whereby the diameter is 20 mm and the thickness is 1.6.
A 2016-type coin-type lithium polymer battery having a thickness of 2016 mm was produced.

Comparative Example 3 Comparative Example 1 was used as a positive electrode active material.
A coin-type test cell was produced in the same manner as in Example 19 except that the LiFePO ₄ carbon composite produced in the above was used.

Comparative Example 4 Comparative Example 2 was used as a positive electrode active material.
A coin-type test cell was produced in the same manner as in Example 19 except that the LiFePO ₄ carbon composite produced in the above was used.

As described above, the polymer batteries of Example 5 and Comparative Examples 3 and 4 manufactured as described above were
The charge / discharge characteristics test performed on the test cell using the non-aqueous electrolyte was performed in the same manner, and the initial charge / discharge capacity and the capacity retention after 50 cycles were measured to evaluate the battery characteristics.

Table 2 shows the measurement results together with the tap density of the positive electrode active material. In addition, a practical battery is required to have an initial discharge capacity of 140 mAh / g or more and a capacity retention rate of 80% or more. Further, the initial discharge capacity is 150 mAh / g or more, and the capacity retention rate is 90
% Is more preferable.

[0152]

[Table 2]

From Table 3, it can be seen that, in synthesizing the LiFePO ₄ carbon composite, an example in which the tap density of the raw material for synthesis after milling was 0.4 g / cc or more and 2.0 g / cc was used. It was confirmed that the nonaqueous electrolyte battery of No. 19 had improved discharge capacity and improved cycle characteristics even when a gel electrolyte was used instead of the nonaqueous electrolyte as the nonaqueous electrolyte.

[0154]

As described above in detail, according to the method for producing a positive electrode active material according to the present invention, the general formula Li _x Fe _1-y
M _y PO ₄ (In the formula, 0.05 ≦ x ≦ 1.2,0 ≦ y
≦ 0.8, M is Mn, Cr, Co, Cu, Ni,
At least one of V, Mo, TI, Zn, Al, Ga, Mg, B, and Nb. A) a mixing step of mixing the synthetic raw materials of the compound represented by the above, a milling step of milling the mixture obtained in the mixing step, and a firing step of firing the mixture milled in the milling step, In addition, the carbon material is added in any of the above steps, and after the milling step, the tap density of the synthetic raw material is set to 0.4 g / cc or more and 2.0 g / cc or less, so that the synthetic raw material is sufficiently refined. In addition, a contact area where the synthetic raw materials contact each other in the firing step can be sufficiently secured. Therefore, according to this method for producing a positive electrode active material, the reaction efficiency of the synthesis reaction is high in the firing step, and Li _x Fe _{1- y My}
The single-phase synthesis of the PO ₄ carbon composite can be reliably performed. As a result, a cathode active material containing no impurities and realizing excellent battery characteristics is manufactured.

According to the method for manufacturing a non-aqueous electrolyte battery according to the present invention, a non-aqueous electrolyte battery is manufactured using the positive electrode active material manufactured as described above. It is possible to manufacture a nonaqueous electrolyte battery having excellent characteristics.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration example of a nonaqueous electrolyte battery to which the present invention is applied.

FIG. 2 is a characteristic diagram showing a Raman spectrum peak of a carbon material.

FIG. 3 is a schematic diagram showing a measuring device used for measuring a tap density of a synthesis raw material of a positive electrode active material.

FIG. 4 is a front view showing a metal tube and a test tube of the measuring device.

FIG. 5 is a side view showing a metal tube and a rotary blade of the measuring device.

[Explanation of symbols]

1 Non-aqueous electrolyte battery, 2 negative electrode, 3 negative electrode can, 4 positive electrode, 5 positive electrode can, 6 separator, 7 insulating gasket

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 10/40 H01M 10/40 A (72) Inventor Junji Hisayama 7-35 Kita Shinagawa, Shinagawa-ku, Tokyo No. within Sony Corporation (72) Inventor Mamoru Hosoya 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo F-term within Sony Corporation (reference) 5H029 AJ03 AJ05 AK03 AL12 AM03 AM04 AM05 AM07 AM16 BJ03 BJ16 CJ02 CJ08 DJ08 DJ16 EJ04 EJ12 HJ02 HJ08 5H050 AA07 AA08 AA19 BA17 CA07 CB12 DA02 DA10 EA10 EA24 FA17 GA02 GA05 GA10 HA02 HA08

Claims (6)

[Claims] 1. A general formula _{Li x Fe 1-y M y} PO 4 ( In the formula, a 0.05 ≦ x ≦ 1.2,0 ≦ y ≦ 0.8, M
Is Mn, Cr, Co, Cu, Ni, V, Mo, TI, Z
At least one of n, Al, Ga, Mg, B, and Nb. A) a mixing step of mixing the synthetic raw materials of the compound represented by the above, a milling step of milling the mixture obtained in the mixing step, and a firing step of firing the mixture milled in the milling step, A carbon material is added in any one of the above steps, and after the milling step, the tap density of the synthesis raw material is set to 0.4 g / cc or more and 2.0 g / cc or less. Production method. As the compound represented by wherein the general formula _{Li x Fe 1-y M y} PO 4, represented by the general formula Li _x FePO ₄ (In the formula, is 0 <x ≦ 1.) The method for producing a positive electrode active material according to claim 1, wherein the compound is synthesized. 3. A method for producing a non-aqueous electrolyte battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte. Li _x Fe _1-y M
_y PO ₄ (where 0.05 ≦ x ≦ 1.2, 0 ≦ y ≦
0.8, and M is Mn, Cr, Co, Cu, Ni,
At least one of V, Mo, TI, Zn, Al, Ga, Mg, B, and Nb. A) a mixing step of mixing the synthetic raw materials of the compound represented by the above, a milling step of milling the mixture obtained in the mixing step, and a firing step of firing the mixture milled in the milling step. And a carbon material is added in any of the above steps, and after the milling step, the tap density of the synthetic raw material is set to 0.4 g / cc or more and 2.0 g / cc or less. Manufacturing method. As the compound represented by wherein the general formula _{Li x Fe 1-y M y} PO 4, represented by the general formula Li _x FePO ₄ (In the formula, is 0 <x ≦ 1.) The method for producing a nonaqueous electrolyte battery according to claim 3, wherein the compound is synthesized. 5. The method for producing a non-aqueous electrolyte battery according to claim 3, wherein the non-aqueous electrolyte is a liquid electrolyte. 6. The method for producing a non-aqueous electrolyte battery according to claim 3, wherein the non-aqueous electrolyte is a polymer electrolyte.