JP2007073344A - Lithium ion secondary battery and electric automobile using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery having electrode composition same as that of conventional lithium ion secondary battery (having large particle diameter) for general use, capable of securing a battery capacity same as that of the conventional one, and to provide an electric automobile using the same. <P>SOLUTION: The lithium ion secondary battery has a cathode and/or an anode of which porosity is 38% or lower and average particle diameter D50 of activator material is 1μm or less. The cathode and the anode are constituted of activator by 80% or more and conductive assistant by 10% or less. An electrode, formed by successively laminating an activator layer having film thickness of 30μm or less and a current collector layer, is provided. Lithium-transition metal oxide is contained in cathode activator, and carbon material or lithium-transition metal compound is contained in anode activator. The lithium ion secondary battery is mounted on the electric automobile as a driving power source. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery and an electric vehicle using the same, and more specifically, a lithium ion secondary battery that can contribute to the development of high output characteristics that could not be realized by a conventional secondary battery, and the same. The present invention relates to an electric vehicle using the.

Conventionally, secondary batteries for automobiles have been required to have higher output characteristics (see, for example, Patent Documents 1 and 2).
Japanese Patent Laid-Open No. 2004-111242 Japanese Patent Laid-Open No. 11-329406

In addition, conventional consumer lithium ion secondary batteries are capacity-oriented and are not suitable for high-power automobile batteries (see, for example, Patent Documents 3 to 6).
JP 2004-319105 A JP 2004-103280 A JP 2003-068299 A Japanese Patent Application No. 2002-572660

On the other hand, a lithium ion battery using a particle size-reduced active material electrode can be designed as a HEV battery having a higher output than current consumer lithium ion batteries.
However, since the contact point between the active materials is increased in the small particle size electrode, it is necessary to reduce the conductive network resistance.

As a countermeasure, the conductive network resistance is reduced by increasing the amount of the conductive additive in the electrode.
However, when the blending amount of the conductive assistant is increased, there is a problem that the amount of the active material in the electrode is decreased and the battery capacity is decreased.

  The present invention has been made in view of such problems of the prior art, and its object is an electrode composition similar to that of a conventional (large particle size) consumer lithium ion secondary battery, and An object of the present invention is to provide a lithium ion secondary battery capable of securing the same battery capacity and an electric vehicle using the same.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by reducing the electrode density (porosity) of the small particle size electrode to reduce the conductive network resistance. The headline and the present invention were completed.

  That is, the lithium ion secondary battery of the present invention is characterized in that, in the positive electrode and / or the negative electrode, the porosity is 38% or less and the average particle diameter D50 of the active material is 1 μm or less.

  Moreover, the suitable form of the lithium ion secondary battery of the present invention is characterized in that the electrode composition of the positive electrode and / or the negative electrode is, in terms of mass, the active material is 80% or more and the conductive assistant is 10% or less. And

  Furthermore, another preferred embodiment of the lithium ion secondary battery of the present invention includes an electrode formed by sequentially laminating an active material layer and a current collector layer from the electrolyte side, and the thickness of the active material layer is 30 μm or less. It is characterized by that.

  Furthermore, in another preferred embodiment of the lithium ion secondary battery of the present invention, the positive electrode active material includes a lithium-transition metal oxide, and the negative electrode active material includes a carbon material or a lithium-transition metal compound. It is characterized by that.

  Moreover, the electric vehicle of the present invention is characterized in that the lithium ion secondary battery is mounted as a driving power source.

  According to the present invention, since the conductive network resistance is reduced by reducing the electrode density (porosity) of the small particle size electrode, the same electrode as that of a conventional (large particle size) consumer lithium ion secondary battery A lithium ion secondary battery having a composition and capable of securing the same battery capacity is obtained.

  Hereinafter, the lithium ion secondary battery of the present invention will be described in detail. In the claims and the specification, “%” represents a mass percentage unless otherwise specified.

  In the lithium ion secondary battery of the present invention, the porosity of one or both of the positive electrode and the negative electrode sandwiching the electrolyte is 38% or less. Moreover, the average particle diameter D50 of the active material of either one or both of the positive electrode and the negative electrode is set to 1 μm or less.

Thus, by using a very small active material having an average particle diameter D50 (50% cumulative particle diameter) of 1 μm or less, the electrode reaction surface area per volume increases and the reaction resistance decreases.
As a method for forming the electrode active material into fine particles, for example, methods such as jet mill pulverization, wet bead mill pulverization, and wet pressure collision pulverization can be appropriately employed.

In addition, by reducing the porosity in the electrode to 38% or less, the contact resistance between the particles can be reduced, the voltage drop at the initial stage of large current discharge can be reduced, and the battery output characteristics are improved.
Although it depends on the combination of electrode constituent materials, a lithium ion secondary battery equipped with an electrode using an active material with a reduced particle size can form a conductive network by reducing the porosity in the electrode to 38% or less, and the contact resistance It is possible to achieve both the effect of reducing the reaction and the effect of increasing the reaction effective active material.

The porosity is as follows:
Porosity [%] = (1-electrode density / theoretical electrode density) × 100
Electrode density [g / cc]: coating amount per unit area of slurry / electrode thickness theoretical electrode density [g / cc]: Σ (electrode material true density × inside electrode composition ratio)
Say.

More preferably, the porosity in the electrode is 33% or less.
In this case, more conductive networks can be formed, and the effect of reducing the contact resistance and the effect of increasing the reaction active active material are likely to increase.
Furthermore, the porosity in the electrode is particularly preferably 15 to 33%.
At this time, it is particularly easy to handle, an extremely large number of conductive networks can be formed, and the effect of reducing the contact resistance and the effect of increasing the reaction effective active material are likely to become extremely large.

In the lithium ion secondary battery of the present invention, the electrode composition of one or both of the positive electrode and the negative electrode is preferably 80% or more of the active material and 10% or less of the conductive auxiliary agent in terms of mass.
Thus, a high capacity, high output lithium ion secondary battery can be constructed by designing a battery with an electrode composition similar to that of a conventional consumer lithium ion secondary battery that emphasizes high capacity.

Here, the positive electrode active material preferably includes a lithium-transition metal oxide, and the negative electrode active material preferably includes a carbon material or a lithium-transition metal compound.
By using a material related to each electrode active material, a lithium ion secondary battery excellent in battery capacity and output characteristics can be constructed.

Further, as the conductive auxiliary agent, typically, a carbon material containing one or both of carbon black and graphite can be used.
At this time, the conductivity in the electrode is ensured, and high output can be obtained when used in a secondary battery.
The particle size of the conductivity-imparting agent is desirably 10 nm to 100 μm, and the same treatment as that for the electrode active material can be adopted as a method for forming fine particles.

  Examples of the carbon black include acetylene black, ketjen black, and furnace black. Examples of the graphite include flake-like and fibrous graphite. These may be naturally derived or artificial. May be good.

Further, as the electrolyte used in the lithium ion secondary battery of the present invention, typically, a liquid electrolyte, a polymer electrolyte, a gel electrolyte, and an arbitrary combination thereof can be used.
Preferably, a polymer electrolyte or a gel electrolyte is used. Polymer electrolytes and gel electrolytes are effective because they are less flammable than liquid electrolytes and are excellent in battery safety at high temperatures.

  Examples of the liquid electrolyte include those in which a supporting salt is dissolved in a non-aqueous solvent, such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), γ-butyllactone ( BL) and the like, and non-aqueous solvents in which one or more are combined and supporting salts such as LiClO4, LiPF6, LiBF4, and LiAsF6.

Examples of the polymer electrolyte include solid polymers such as polyethylene oxide (PEO), polypropylene oxide (PPO), polyvinylidene difluoride (PVDF), and copolymers thereof, LiPF6, LiBF4, and LiN (SO ₂ C). Supporting salts such as ₂ F ₃ ) ₂ and LiN (SO ₂ C ₂ F ₅ ) ₂ are listed.

Examples of the gel electrolyte include non-aqueous solvents such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and γ-butyl lactone (BL) alone or in combination. (Plasticizer) and solid polymers such as polyethylene oxide (PEO), polypropylene oxide (PPO), polyvinylidene difluoride (PVDF), and copolymers thereof, and LiPF6, LiBF4, LiN (SO ₂ C ₂ F ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) _{2 and the} like.
In addition, what is necessary is just to determine the weight ratio of the solid polymer and electrolyte solution in a gel electrolyte according to the intended purpose etc., but it is the range of 2: 98-90: 10.

In the lithium ion secondary battery of the present invention, either one or both of the positive electrode and the negative electrode can be formed by sequentially laminating an active material layer and a current collector layer from the electrolyte side. FIG. 1 shows a battery element in which both a positive electrode and a negative electrode have a two-layer structure of an active material layer and a current collector layer.
From the viewpoint of using such a two-layer structure in a secondary battery for HEV, the thickness of the active material layer is preferably 30 μm or less.

As a result, the diffusion resistance can be reduced, which can be effective in increasing the capacity utilization rate and improving the output characteristics during large current discharge.
In addition, it is possible to design a high-capacity battery as the electrode film thickness is thicker. However, as in the present invention product, using a small particle size active material, a conventional lithium ion secondary for consumer use that emphasizes the high capacity of the battery. When the electrode composition is the same as that of the battery, lithium ion diffusion from the electrolytic solution during large current discharge tends to occur.

As a constituent material of the current collector layer, for example, aluminum, copper, or stainless steel, and a metal foil or alloy foil according to any combination thereof can be used.
In this case, since an electrode can be manufactured by applying a slurry containing an active material having a small particle diameter and a conductivity-imparting agent to the metal foil or alloy foil as the electrode current collector, productivity is improved.

Next, the electric vehicle of the present invention will be described in detail.
As described above, the electric vehicle of the present invention includes the lithium ion secondary battery mounted as a driving power source.
That is, a high-output and high-capacity lithium ion secondary battery in which the porosity in the electrode is controlled and the particle diameter of the electrode constituent material is finer is applied, so that a high-output vehicle is obtained.
The electric vehicle of the present invention includes the above-described lithium ion secondary battery as a power source, and includes a “hybrid car” that can travel in combination with other power sources.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in full detail, this invention is not limited to these Examples.

Example 1
A solid content obtained by mixing Li- (Ni-Co-Al) -based composite oxide having a particle diameter of 0.8 μm, acetylene black, and PVDF at a weight ratio of 80:10:10 is dissolved in a solvent NNP to obtain a positive electrode slurry. Produced.
This positive electrode slurry was applied to an Al foil (film thickness: 20 μm) as a positive electrode current collector with a basis weight of 3 mg / cm 2 by a self-propelled die coater and pressed to a porosity of 33% to obtain a positive electrode.

A solid content obtained by mixing hard carbon having a particle size of 5 μm, VGCF, and PVDF at a weight ratio of 85: 5: 10 was dissolved in a solvent NMP to prepare a negative electrode slurry.
This negative electrode slurry was applied to a Cu foil (film thickness: 10 μm) as a negative electrode current collector with a basis weight of 1.5 mg / cm 2 by a self-propelled die coater and pressed to a porosity of 55% to obtain a negative electrode.

The positive electrode and the negative electrode were opposed to each other through a lithium ion battery separator to form a battery element.
This battery element was inserted into a three-side sealed exterior aluminum laminate. Next, after injecting electrolyte solution 1M LiPF6 / EC + PC + DEC (volume ratio 2: 2: 6) for lithium ion battery into aluminate, vacuum sealing is performed so that a tab comes out from the outer packaging material, and a sealed laminated lithium ion battery Was made.

(Example 2)
Self-propelled die coater with a weight per unit area of 3 mg / cm2 of positive electrode slurry formed by mixing Li- (Ni-Co-Al) composite oxide having a particle size of 0.8 [mu] m, acetylene black and PVDF at a weight ratio of 80:10:10 And was pressed to a porosity of 38% to obtain a positive electrode.
Except that this positive electrode was used, the same operation as in Example 1 was repeated to produce a sealed laminate type lithium ion battery.

(Example 3)
Self-propelled die coater with a weight per unit area of 3 mg / cm2 of positive electrode slurry formed by mixing Li- (Ni-Co-Al) composite oxide having a particle size of 0.8 [mu] m, acetylene black and PVDF at a weight ratio of 80:10:10 And was pressed to a porosity of 25% to obtain a positive electrode.
Except that this positive electrode was used, the same operation as in Example 1 was repeated to produce a sealed laminate type lithium ion battery.

Example 4
Self-propelled die coater with a weight per unit area of 3 mg / cm2 of positive electrode slurry formed by mixing Li- (Ni-Co-Al) composite oxide having a particle size of 0.8 [mu] m, acetylene black and PVDF at a weight ratio of 80:10:10 And was pressed to a porosity of 20% to obtain a positive electrode.
Except that this positive electrode was used, the same operation as in Example 1 was repeated to produce a sealed laminate type lithium ion battery.

(Example 5)
Self-propelled die coater with a weight per unit area of 3 mg / cm2 of positive electrode slurry formed by mixing Li- (Ni-Co-Al) composite oxide having a particle size of 0.8 [mu] m, acetylene black and PVDF at a weight ratio of 80:10:10 And was pressed to a porosity of 15% to obtain a positive electrode.
Except that this positive electrode was used, the same operation as in Example 1 was repeated to produce a sealed laminate type lithium ion battery.

(Example 6)
A positive electrode slurry prepared by mixing spinel lithium manganate having a particle diameter of 0.7 μm, acetylene black, and PVDF at a weight ratio of 80:10:10 was applied at a basis weight of 4 mg / cm 2 using a self-propelled die coater, and a porosity of 33 % Was pressed to obtain a positive electrode.
Except that this positive electrode was used, the same operation as in Example 1 was repeated to produce a sealed laminate type lithium ion battery.

(Comparative Example 1)
Self-propelled die coater with a weight per unit area of 3 mg / cm2 of positive electrode slurry formed by mixing Li- (Ni-Co-Al) composite oxide having a particle size of 0.8 [mu] m, acetylene black and PVDF at a weight ratio of 80:10:10 And was pressed to a porosity of 48% to obtain a positive electrode.
Except that this positive electrode was used, the same operation as in Example 1 was repeated to produce a sealed laminate type lithium ion battery.

(Comparative Example 2)
The positive electrode of the electrode of the lithium ion battery is a positive electrode slurry obtained by mixing Li- (Ni-Co-Al) -based composite oxide having a particle diameter of 5 μm, acetylene black, and PVDF at a weight ratio of 80:10:10. A positive electrode was obtained by coating with a self-propelled die coater at / cm 2 and pressing to a porosity of 33%.
Except that this positive electrode was used, the same operation as in Example 1 was repeated to produce a sealed laminate type lithium ion battery.

(Comparative Example 3)
Using a self-propelled die coater with a weight of 3 mg / cm 2 of a positive electrode slurry formed by mixing Li— (Ni—Co—Al) composite oxide having a particle size of 5 μm, acetylene black, and PVDF at a weight ratio of 80:10:10 Then, pressing was performed to obtain a porosity of 38% to obtain a positive electrode.
Except that this positive electrode was used, the same operation as in Example 1 was repeated to produce a sealed laminate type lithium ion battery.

(Comparative Example 4)
Using a self-propelled die coater with a weight of 3 mg / cm 2 of a positive electrode slurry formed by mixing Li— (Ni—Co—Al) composite oxide having a particle size of 5 μm, acetylene black, and PVDF at a weight ratio of 80:10:10 Then, pressing was performed so that the porosity was 46% to obtain a positive electrode.
Except that this positive electrode was used, the same operation as in Example 1 was repeated to produce a sealed laminate type lithium ion battery.

(Comparative Example 5)
A positive electrode slurry made by mixing lithium nickelate having a particle diameter of 5 μm, acetylene black, and PVDF at a weight ratio of 80:10:10 is applied at a basis weight of 3 mg / cm 2 using a self-propelled die coater, resulting in a porosity of 52%. A positive electrode was obtained.
Except that this positive electrode was used, the same operation as in Example 1 was repeated to produce a sealed laminate type lithium ion battery.

(Comparative Example 6)
Using a self-propelled die coater with a weight of 3 mg / cm 2 of a positive electrode slurry formed by mixing Li— (Ni—Co—Al) composite oxide having a particle size of 5 μm, acetylene black, and PVDF at a weight ratio of 80:10:10 Then, pressing was performed so that the porosity was 25% to obtain a positive electrode.
Except that this positive electrode was used, the same operation as in Example 1 was repeated to produce a sealed laminate type lithium ion battery.

(Comparative Example 7)
Using a self-propelled die coater with a weight of 3 mg / cm 2 of a positive electrode slurry formed by mixing Li— (Ni—Co—Al) composite oxide having a particle size of 5 μm, acetylene black, and PVDF at a weight ratio of 80:10:10 Then, pressing was performed to obtain a porosity of 15% to obtain a positive electrode.
Except that this positive electrode was used, the same operation as in Example 1 was repeated to produce a sealed laminate type lithium ion battery.

(Comparative Example 8)
A positive electrode slurry prepared by mixing spinel lithium manganate having a particle diameter of 10 μm, acetylene black, and PVDF at a weight ratio of 80:10:10 was applied at a basis weight of 4 mg / cm 2 using a self-propelled die coater, and the porosity was 33%. A positive electrode was obtained by pressing.
Except that this positive electrode was used, the same operation as in Example 1 was repeated to produce a sealed laminate type lithium ion battery.

(Evaluation)
The charging / discharging test was done with each battery of Examples 1-6 and Comparative Examples 1-8.
In the experiment, after initial charge at a current of 0.2 C, discharge at 0.5 C, and after performing a 10-cycle charge / discharge test at 1 C, rate characteristics and AC with a full charge (4.2 V) of 100 C (20 mA / cm 2 or more) Reaction resistance due to impedance was evaluated.

When Example 1 and Comparative Example 2 in FIG. 2 were compared, the initial IR drop resistance values were almost the same in the 100 C rate characteristics.
On the other hand, when Example 1 and Comparative Example 2 in FIG. 3 were compared, the capacity utilization was better in Example 1 with a smaller particle size.
From this, it was confirmed that a high-power battery can be designed with a small particle size electrode having a porosity of 33% or less.

From Tables 1 and 3, in Example 6 and Comparative Example 8 in which spinel lithium manganate was used as the positive electrode active material, when comparing the IR drop resistance values, both the initial IR drop resistance value and the capacity utilization rate were 100 C rate characteristics. In both cases, Example 6 having a smaller particle diameter was superior.
From this, it was confirmed that a high-power battery can be designed with a small particle size electrode having a porosity of 33% regardless of the type of positive electrode material.

From Tables 1 and 2 of Examples 1 to 5, in the small-diameter electrode, in the region where the porosity exceeds 33%, the initial IR drop resistance value increases with increasing porosity, and the porosity is less than 33%. The IR drop resistance did not decrease, but the IR drop resistance value was found to be smaller than that of the conventional electrode.
From this, it was found that a small conductive electrode having the same electrode composition and battery capacity as in the prior art forms a good conductive network with a porosity of 33% or less.

Further, from Table 2 and Comparative Examples 2 to 7 in FIG. 2, it was found that in the electrode having a large particle size, there was no change in the initial IR drop resistance value as the porosity increased.
From this, it was found that in the electrode having a large particle size, a sufficient conductive network was formed in the electrode even when the porosity was large.

Further, from Comparative Examples 2 to 7 in FIG. 4, in the AC impedance measurement, when the particle size is large, the dependence of the reaction resistance on the porosity is not observed.
From this, it was confirmed that the conductive network was formed at any porosity.

On the other hand, from Example 2 in FIG. 4, when the particle size is small, the reaction resistance becomes larger than that of the electrode having a large particle size when the porosity exceeds 38%.
From this, it was found that when the particle size is small, the formation of the conductive network is reduced when the porosity is more than 38%, and only some of the particles are involved in the reaction, thereby increasing the reaction resistance.

In addition, from Examples 1 and 3 to 5 in FIG. 4, since the reaction resistance did not show porosity dependency, it was confirmed that a favorable conductive network was formed at a porosity of 33% or less.
Further, when Example 1 and Comparative Example 2 with a conductive network are compared, and Example 6 and Comparative Example 8 are compared, the reaction resistance can be reduced by using a small particle size electrode, and the porosity is 33% or less. It has been found that a battery with a small particle size electrode can be designed with a high output.

It is a schematic sectional drawing which shows an example of a lithium ion secondary battery. It is a graph which shows the relationship between a porosity and IR drop resistance. It is a graph which shows the relationship between a porosity and a capacity utilization rate. It is a graph which shows the relationship between a porosity and relative reaction resistance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode active material layer 2 Positive electrode collector 3 Negative electrode collector 4 Negative electrode active material layer 5 Separator containing electrolyte solution

Claims (8)

  A lithium ion secondary battery, wherein the positive electrode and / or the negative electrode have a porosity of 38% or less and an average particle diameter D50 of the active material of 1 μm or less.   The lithium ion secondary battery according to claim 1, wherein a porosity of the positive electrode and / or the negative electrode is 33% or less.   3. The lithium ion secondary battery according to claim 1, wherein a porosity of the positive electrode and / or the negative electrode is 15 to 33%.   The electrode composition of the positive electrode and / or the negative electrode is, in terms of mass, the active material is 80% or more and the conductive auxiliary is 10% or less, according to any one of claims 1 to 3. Lithium ion secondary battery.   The lithium ion secondary according to claim 1, comprising an electrode formed by sequentially laminating an active material layer and a current collector layer from the electrolyte side, wherein the active material layer has a thickness of 30 μm or less. battery.   The lithium ion secondary battery according to claim 1, wherein the positive electrode active material includes a lithium-transition metal oxide, and the negative electrode active material includes a carbon material or a lithium-transition metal compound.   The lithium ion secondary battery according to claim 1, wherein the electrolyte is at least one selected from the group consisting of a liquid electrolyte, a polymer electrolyte, and a gel electrolyte.   An electric vehicle comprising the lithium ion secondary battery according to any one of claims 1 to 7 mounted as a driving power source.

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