JP3511517B2 - Lithium secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium secondary battery. More specifically, the present invention relates to a lithium secondary battery having a low internal resistance, an excellent large current output characteristic, a large volume energy density, and a constant quality.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries have come to be widely used as power source batteries for portable electronic devices such as mobile phones, VTRs, and notebook computers. In addition, since the lithium secondary battery has a cell voltage of about 4 V, which is higher than that of conventional secondary batteries such as lead storage batteries, and has a large energy density, not only the portable electronic device but also recent environmental problems. Against this background, electric vehicles (E
V) or a hybrid electric vehicle (HEV) as a motor drive power source.

In a lithium secondary battery, generally, a lithium transition metal composite oxide is used as a positive electrode active material, a carbonaceous material is used as a negative electrode active material, and an Li electrolyte is dissolved in an organic solvent as an electrolyte. There are various types of electrode bodies, such as a sandwich type, a wound type, and a laminated type, as an electrode body that is a part that performs a battery reaction.

Among these, in a lithium secondary battery having a relatively large capacity, which is preferably used for EV and the like, as shown in FIG. 1, a current collecting tab (a role of a lead wire for collecting current from an electrode) the play. hereinafter referred to as "tabs".) 5 is mounted with the positive and negative electrode plates 2 and 3 (the positive electrode plate 2, a negative electrode plate 3), so as not to contact with each other while a separator 4 between, cylindrical A wound-type electrode body 1 (hereinafter, referred to as a “wound body”) wound around the outer periphery of the winding core 6 is preferably used.

The electrode plates 2 and 3 are formed by forming a layer of an electrode active material (which indicates both a positive electrode active material and a negative electrode active material) on both surfaces of a current collecting substrate such as a metal foil, and are collected from a plurality of locations. Electrify
Therefore, the tabs 5 are formed on the end portions of the electrode plates 2 and 3 using a means such as ultrasonic welding during the work of winding the electrode plates 2 and 3 and the separator 4 around the winding core 6. It can be attached to the exposed portion of the foil at predetermined intervals.

Here, the electronic conduction resistance of the wound body (hereinafter,
It is called "resistance". ) Is greatly affected by the positive electrode active material, which has a smaller electronic conductivity than other members. Therefore, how to form the positive electrode active material layer so as to have a low resistance is a key for realizing a low internal resistance and a high output battery.

It is not difficult to imagine that the resistance of the positive electrode plate is greatly affected by the bulk density of the positive electrode active material layer. That is, the higher the bulk density, the larger the contact area between the positive electrode active material powders, which is considered to be preferable for reducing the resistance. Further, it is preferable to add carbon fine powder such as acetylene black or carbon black to the positive electrode active material for the purpose of improving conductivity, but even in such a case, by increasing the bulk density, carbon fine powder is obtained. It is considered that good contact with the positive electrode active material powder is achieved and the resistance is reduced. Furthermore, if the bulk density is large, the volume of the positive electrode active material layer is small, and the battery can be made compact. Here, in the step of increasing the bulk density of the positive electrode active material layer, the morphology of the particles of the positive electrode active material layer is not destroyed, and the current collecting substrate is not damaged or deformed such as wrinkles. The process conditions for high density must be optimized.

On the other hand, the contact area between the positive electrode active material layer and the nonaqueous electrolytic solution must be appropriately secured so that the movement of Li ions between the positive electrode active material and the nonaqueous electrolytic solution also proceeds smoothly. I won't. Therefore, from this viewpoint, the positive electrode active material layer needs to have an appropriate amount of pores.

Here, as a candidate for a practical positive electrode active material, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), and lithium manganate (L
Examples thereof include lithium transition metal composite oxides such as iMnO ₂ and LiMn ₂ O ₄ ). Needless to say, the electron conductivity varies depending on the substance and composition, and as disclosed by the inventors, The output characteristics also differ depending on the type of positive electrode active material (Japanese Patent Application No. 10-3181).
09).

Further, LiCoO₂And LiNiO₂, Li
MnO₂Is the space group R3-m ("-" is usually the upper part of "3")
Attached to indicate reversion. ), But LiMn ₂O_FourIs
It has a spinel structure belonging to the space group Fd3m.
There is a difference in the particle morphology based on the difference in the crystal system such as
Cheat. If the particle morphology is different, such as fine carbon powder to be added
The amount of conductive aid and binder also changes. Therefore, low resistance
The range of the bulk density that the positive electrode active material layer should satisfy is the positive electrode active material.
Different will be correspondingly different.

Note that Li and Co are mainly used as the positive electrode active material.
Although the technical information on the “apparent density” to be satisfied by the positive electrode active material layer in the case of using the composite oxide composed of (1) has been already disclosed (see Patent Document 1), the one disclosed here is a high capacity battery. It is intended for realization and there is no mention of reducing the internal resistance of the battery.

[0012]

[Patent Document 1] Japanese Unexamined Patent Publication No. 5-74494

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has a low internal resistance, an excellent large current output characteristic, a large volume energy density, and a constant quality lithium. It is intended to provide a secondary battery. Note that, as will be described later, the present invention intentionally uses lithium manganate having a spinel structure having a smaller lithium capacity per unit weight than lithium cobalt oxide as a positive electrode active material, and thus, as in the invention described in Patent Document 1, It is an object of the present invention to provide a battery having a low internal resistance and a high output, without the main purpose of increasing the capacity.

[0014]

According to the present invention, a positive electrode plate and a negative electrode plate, each of which has a positive electrode active material layer or a negative electrode active material layer formed on a current collecting substrate, are provided with a separator as a core. A lithium secondary battery comprising a wound electrode body wound around an outer periphery, wherein lithium (Li) and manganese (Mn) are used as a positive electrode active material constituting the positive electrode active material layer.
Lithium manganate having a cubic spinel structure and having a Li / Mn ratio of more than 0.5 as a main component is used.
Rutotomoni, as the positive electrode plate, said at bulk density of the positive electrode active material layer is 2 g / cm ³ or more 3.5 g / cm ³ or less, the positive electrode active material layer is formed on at least one end of the width direction of the current collector substrate Not collecting stripe structure and collecting current from multiple points
In addition, the winding length in the winding direction is 1 m or more , and the internal resistance is 5 m.
Provided is a lithium secondary battery having a resistance of Ω or less .

The positive electrode active material layer formed on the positive electrode plate used in the lithium secondary battery of the present invention has 1 to 10 parts by weight of carbon fine powder and 1 to 10 parts by weight of organic substance with respect to 100 parts by weight of lithium manganate. It is preferably composed of parts. On the other hand, it is preferable to use highly graphitized carbon fiber as the negative electrode active material in the negative electrode plate.

The present invention is preferably applied when the battery capacity is 2 Ah or more, and the lithium secondary battery of the present invention is preferably used as a power source for an electric vehicle or a hybrid electric vehicle.

[0017]

Embodiments of the present invention will be described below with reference to the drawings, but it goes without saying that the present invention is not limited to the following embodiments.

The lithium secondary battery of the present invention has been previously described with reference to FIG.
As shown in, to collect current from multiple locations
A wound electrode body in which positive and negative electrode plates (positive electrode plate 2 and negative electrode plate 3) each having a plurality of current collecting tabs 5 (tabs) attached thereto are wound around the outer circumference of the winding core 6 via the separator 4. (Wound body) 1 is a lithium secondary battery obtained by impregnating a non-aqueous electrolytic solution.

The positive electrode plate 2 is manufactured by applying a positive electrode active material on both surfaces of a current collecting substrate. As the current collector substrate, a metal foil such as an aluminum foil or a titanium foil having good corrosion resistance against a positive electrode electrochemical reaction is used, but a punching metal or a mesh (mesh) may be used instead of the foil.

In the present invention, as the positive electrode active material, among various lithium-transition metal composite oxides, a cubic represented by LiMn ₂ O ₄ having a stoichiometric composition represented by LiMn ₂ O ₄ is more than 0.5. Lithium manganate having a crystalline spinel structure (hereinafter referred to as "lithium manganate spinel") is used. Lithium manganate spinel
Compared with lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), the lithium capacity is small, but the electron conductivity is large, and the decrease in output is small even when the discharge depth is deep, It is especially excellent as a high-power battery material.

The lithium manganate spinel is
Such stoichiometry is not limited to those of the composition, by replacing part of Mn with one or more other elements, the general formula _{LiM X Mn 2-X O 4} (M is a substituted element, X is Lithium manganate spinel represented by (representing the amount of substitution) is also preferably used. In the lithium manganate spinel which has been subjected to such element substitution, the Li / Mn ratio exceeds 0.5.

The substituting element M is listed below by the element symbols, but Li, Fe, Mn, Ni, Mg, Zn,
B, Al, Co, Cr, Si, Ti, Sn, P, V, S
b, Nb, Ta, Mo, and W can be mentioned, and theoretically, Li has a +1 valence, and Fe, Mn, Ni, Mg, and Zn have +.
Divalent, B, Al, Co, Cr +3, Si, Ti, S
n is +4 valence, P, V, Sb, Nb, Ta is +5 valence, M
o and W are +6 valent ions and are elements that form a solid solution in LiMn ₂ O ₄ . However, when Co and Sn are +2 valence, and when Fe, Sb and Ti are +3 valence, M
+3 valence for n, +4 valence for Cr, + for Cr
It may be tetravalent or +6.

Therefore, the various substitution elements M may exist in a state having mixed valences, and the amount of oxygen needs to be 4 as represented by the stoichiometric composition. Alternatively, it may be deficient or excessively present within the range for maintaining the crystal structure.

Hereinafter, it is assumed that lithium manganate spinel is used as the positive electrode active material. Positive electrode active material,
That is, the lithium manganate spinel is applied to the current collector substrate (metal foil) by using a slurry or paste (hereinafter referred to as “slurry or the like”) prepared by adding a solvent, a binder and the like to lithium manganate spinel powder. It is performed by coating and drying the current collecting substrate using a roll coater method or the like. In forming the positive electrode active material layer, fine carbon powder such as acetylene black or carbon black is added to the lithium manganate spinel powder as a conduction aid.

The composition of the obtained positive electrode active material layer is usually
It is composed of 1 to 10 parts by weight of carbon fine powder and 1 to 10 parts by weight of organic matter with respect to 100 parts by weight of lithium manganate as a positive electrode active material. If the carbon fine powder is less than 1 part by weight, it may not exert the effect of reducing the resistance. On the other hand, if it exceeds 10 parts by weight, it becomes difficult to prepare a slurry or the like, and the amount of the binder added in preparing the slurry or the like is extremely high. However, there is a problem in that it may lead to an increase in resistance.

The amount of the organic substance is almost equal to the amount of the binder, but it includes the amount of the organic solvent used when the slurry or the like was prepared and adsorbed on the lithium manganate spinel, and the amount of the organic solvent bound to the binder. It is a waste. If the amount of the organic substance (mainly the binder) is 1 part by weight or less, the positive electrode active material layer may not have sufficient strength and flexibility. On the other hand, the organic substance (mainly the binder) is an insulator, and therefore 10 parts by weight. If it is more than 1 part, the resistance of the positive electrode active material layer may increase.

On the other hand, the negative electrode plate 3 can be manufactured in the same manner as the positive electrode plate 2. As the current collecting substrate of the negative electrode plate 3, a metal foil such as a copper foil or a nickel foil having a good corrosion resistance against a negative electrode electrochemical reaction is preferably used. As the negative electrode active material, an amorphous carbonaceous material such as soft carbon or hard carbon, or highly graphitized carbonaceous powder such as artificial graphite or natural graphite is used. Of these, highly graphitized carbon fibers are preferably used in the present invention.

As the separator 4, a Li ion permeable polyethylene film (PE having micropores) is used.
A film having a three-layer structure in which a porous Li ion permeable polypropylene film (PP film) is sandwiched is preferably used. This is because the PE film is softened at about 130 ° C. and the micropores are crushed when the temperature of the wound body rises, and also serves as a safety mechanism for suppressing the movement of Li ions, that is, the battery reaction. Then, by sandwiching this PE film between PP films having a higher softening temperature, even when the PE film is softened,
The PP film retains its shape to prevent contact and short circuit between the positive electrode plate 2 and the negative electrode plate 3, and it is possible to reliably suppress battery reaction and ensure safety.

During the work of winding the electrode plates 2 and 3 and the separator 4 around the winding core 6, a portion of the electrode plates 2 and 3 to which the current collecting substrate not coated with the electrode active material is exposed, The tabs 5 are attached respectively. That is, the electrode plates 2 and 3 have a striped structure in which the positive electrode active material layer is not formed on at least one end in the width direction of the current collector substrate and a plurality of portions.
It has a configuration to collect current from . Further, such a winding operation is suitably adopted when an electrode plate having a length in the winding direction of 1 m or more is used.

As the tab 5, the respective electrode plates 2,
A foil-shaped one made of the same material as the collector substrate 3 is preferably used. The tab 5 can be attached to the electrode plates 2 and 3 by ultrasonic welding, spot welding or the like. At this time, as shown in FIG. 1, if the tabs 5 are attached so that the tabs of one electrode are arranged on one end surface of the wound body 1, contact between the tabs 5 can be prevented, which is preferable. .

In assembling the battery, first, while maintaining electrical continuity with the tab 5 and a terminal for taking out an electric current to the outside, insert the manufactured wound body 1 into the battery case and hold it at a stable position. To do. Then, after impregnating the non-aqueous electrolyte, the battery can be sealed by sealing the battery case. In the present invention, it goes without saying that there is no limitation on the shape or structure of the battery case or the form of connection between the tab 5 and the battery terminal in the wound body 1.

As the non-aqueous electrolyte, hexafluorofluoride is used.
Lithium oxide (LiPF ₆) And lithium borofluoride (L
iBF_Four) Lithium complex fluorine compounds such as
Lithium oxalate (LiClO_Four) Lithium halogen
One or more types of electrolytes selected from
Ethylene carbonate (EC), diethyl carbonate
(DEC), dimethyl carbonate (DMC),
Carbonate ester such as ropylene carbonate (PC)
Solvent, γ-butyrolactone, tetrahydrofuran, acetone
Dissolved in a single solvent such as trinitrile or a mixed solvent
Is preferably used.

Next, the processing of the positive electrode plate, which should be carried out in producing the wound body 1 described above, will be described in more detail. The positive electrode active material layer coated on the current collecting substrate has a large porosity and a small bulk density in a state where it is dried after being coated with a slurry, a slip, or a paste. If the wound body 1 is manufactured in this state, the internal resistance of the wound body 1 becomes large due to the resistance of the positive electrode plate, which makes it extremely difficult to use it as a high-power battery. There is a problem that the volume becomes large and the battery becomes large.

Therefore, it is necessary to increase the bulk density of the positive electrode active material layer and, at the same time, secure the porosity to such an extent that the nonaqueous electrolytic solution is sufficiently impregnated into the positive electrode active material layer. At this time, it is important not to destroy the form of the lithium manganate spinel powder, for example, to prevent the secondary particles from being destroyed. Therefore, in the present invention, the bulk density of the positive electrode active material layer formed by using lithium manganate spinel as the positive electrode active material is 2 g / cm ³ or more and 3.5 g / c or more.
m ³ are below.

In addition, as shown in Examples described later, a positive electrode
The bulk density of the active material layer is 2 g / cm³Resistance if
Variation, and problems in providing stable quality batteries
There is. Also, because the electrode volume is large, the battery is
There is a problem. On the other hand, the positive electrode active material layer has a bulk density of 3.5.
g / cm³In the case of above, there is a problem in the treatment process.
As a result, wrinkles may occur on the current collecting substrate during densification, or the current collecting substrate may
It can be mentioned that damage such as cutting occurs. Also, the positive electrode
The bulk density of the active material layer is 3.5 g / cm ³Even above
The resistance does not decrease significantly, and conversely, impregnation of the non-aqueous electrolyte occurs.
It causes problems such as being difficult to control.

After forming the positive electrode active material layer on the surface of the current collecting substrate by the above-mentioned method, as a method for keeping the bulk density of the positive electrode active material layer within such a predetermined range, a method using a warm roll press is preferable. Used for. The roll temperature in the warm roll press is preferably 80 ° C. or higher and 180 ° C. or lower, and a more preferable temperature range is 100 ° C. or higher and 150 ° C. or lower. When the roll temperature is low, there is a problem that the elasticity of the positive electrode active material layer is large and it may be difficult to achieve high density. On the other hand, when the roll temperature is high, the binder is melted and the positive electrode is compressed. There are problems that the active material layer is crushed and protrudes to the outer periphery, or the positive electrode active material layer is peeled off from the current collecting substrate and adheres to the roll.

The roll diameter is preferably 3 because it is preferable to press the positive electrode active material layer in a plane.
The diameter is preferably not less than 00 mmφ, and is preferably not more than 1000 mmφ from the viewpoint of increasing the size of the roll pressing device and maintaining the parallel accuracy and shape accuracy of the press surface.
The surface material of the roll is preferably hard metal such as hard chrome plating. Roll pressing with a warm roll for such a positive electrode plate can also be used for adjusting the bulk density of the negative electrode active material layer in the negative electrode plate.

The rotation speed of the roll, that is, the feed speed of the positive electrode plate and the roll pressure can be arbitrarily adjusted within a range that allows the bulk density of the electrode active material layer to be within the above range. For example, when the pressure is lowered and the roll pressing is performed a plurality of times, the work process takes time, but damage to the current collecting substrate can be minimized. On the other hand, if the pressure is increased, the number of presses can be reduced, but this may cause a problem such as wrinkles on the current collecting substrate. Further, if the feeding speed of the positive electrode plate is increased, wrinkles are likely to occur on the positive electrode plate, and if the feeding speed is slow, there is a demerit that work time is long. In addition, when performing the roll press in multiple times, the roll temperature of each time,
The press pressure and the feed rate can be arbitrarily changed and determined.

In this way, the bulk density of the positive electrode active material layer can be set within a predetermined range before the wound body 1 is manufactured, but at this time, some wrinkles may occur on the positive electrode plate. There is also. If such a positive electrode plate is excluded as a defect, improvement in production efficiency is not desired. Therefore, it is technically important to manufacture a wound body so that it can be used as a battery as long as it does not affect the battery characteristics even if it has some defects such as wrinkles.

Therefore, in the present invention, as shown in the explanatory view of FIG. 2, the electrode plates 2 and 3 and the separator 4 are
A method of producing a wound-type electrode body by sandwiching the core 6 and the pressure roller 7 and pressing the core 6 while winding the core is also preferably employed. Thus, by forcibly applying pressure during winding, it is possible to forcibly deform the electrode plates such as wrinkles and to wind the electrode plates 2 and 3 at high density. The tabs are omitted in FIG.

Now, in the present invention, there is no limitation on the shape of the battery constituent members other than the constituent member of the wound body, such as the battery case and the external terminals for connecting the battery to an external addition or the like. Absent. INDUSTRIAL APPLICABILITY The lithium secondary battery of the present invention has a low internal resistance and can increase the volume energy density as will be described later. Therefore, it is necessary to frequently discharge a large current in an electric vehicle or a hybrid electric vehicle. It exhibits preferable characteristics as a power source, especially as a power source battery for driving a motor. Since the positive electrode plate used in the present invention has a length in the winding direction of 1 m or more, the present invention is suitably used for a battery having a relatively large battery capacity, specifically, 2 Ah or more.

Hereinafter, the present invention will be described in more detail with reference to Examples.
However, the present invention is limited to the following examples.
Not. As a positive electrode active material,Place a part of Mn with Li
Replaced Li_{1 + X}Mn_2-XO_Four(X = 0.1, Li / Mn =
0.58), Li in which a part of Mn is replaced with Li_{1 + X}M
n_2-XO_Four(X = 0.15, Li / Mn = 0.62),
Li (Ni) obtained by substituting a part of Mn with Ni and Ti
Ti)_XMn_2-XO_Four(X = 0.2, Li / Mn = 0.5
6), L in which a part of Mn is replaced by Mg and Ti
i (MgTi)_XMn_2-XO_Four(X = 0.2, Li / Mn
= 0.56), ofFourKinds of lithium manganate spinel
Was used.

These ~ ofFourMa of different composition
Using lithium nganate spinel, 4 for each material
Acetylene black powder equivalent to 6% by weight, equivalent to 6% by weight
Add binder (PVDF: polyvinylidene fluoride)
And convert them to NMP (N-methyl-2-pyrrolidone)
Disperse evenly (PVDF dissolved in NMP) and slurry
Was produced.

Using this slurry, the weight density of the positive electrode active material layer after forming the positive electrode active material layer was 12 mg on one side.
Both sides were coated on an aluminum foil (collector substrate) having a thickness of 20 μm and a width of 100 mm so that the thickness would be / cm ² . Then, the density of the positive electrode active material layer is increased by warm-rolling the obtained positive electrode plate, and at this time, by changing the warm roll-pressing conditions, various bulk densities of the positive electrode active material layer are different. A positive electrode plate was obtained.

The bulk density of the positive electrode active material layer was calculated from the weight and thickness of a 20 mmφ disc punched out from the positive electrode plate after warm roll pressing. That is, the weight of an aluminum foil having a thickness of 20 μm and a diameter of 20 mmφ is measured in advance, and the weight of the aluminum foil alone is subtracted from the weight of a 20 mmφ sample punched from the positive electrode plate to calculate the weight of the positive electrode active material layer portion. On the other hand, assuming that the change in thickness during warm roll pressing is only in the positive electrode active material layer portion, the thickness of the positive electrode active material layer is subtracted by subtracting 20 μm, which is the thickness of the aluminum foil, from the total thickness of the 20 mmφ sample to obtain the shape of the positive electrode active material layer. The bulk density of the positive electrode active material layer was calculated from the weight. Since this bulk density measuring method is naturally a destructive test, the obtained bulk density value was simultaneously used as a representative value of the positive electrode active material layer in the positive electrode plate manufactured under the same conditions.

On the other hand, the negative electrode plate uses highly graphitized carbon fiber as a negative electrode active material, and 5% by weight of PVDF is added to the negative electrode plate and uniformly dispersed in NMP (PVDF is NM
Dissolving in P) to prepare a slurry, and using a copper foil having a thickness of 10 μm and a width of 100 mm as a current collector substrate, coating, warm roll press treatment and the like are performed in the same manner as in the above-described method for producing a positive electrode plate. It was made by that. Both the positive electrode plate and the negative electrode plate manufactured as described above are stripe-coated with no electrode active material layer formed on at least one end in the width direction in order to attach a current collecting tab.

Regarding the adjustment of the bulk density of the positive electrode active material layer by the roll press of the positive electrode plate described above, first, a case of using a normal room temperature roll press (one that does not preheat the electrode plate or heat the roll) When the bulk density of the positive electrode active material layer after roll pressing reaches 2.2 g / cm ³ or more, the positive electrode plate suddenly deforms like a wave, and fine wrinkles are formed near the boundary between the current collecting substrate and the positive electrode active material layer. There has occurred. In such a wrinkle, in the current collecting substrate, the portion where the positive electrode active material layer is formed expands due to pressure, but the portion where the positive electrode active material layer is not formed expands without applying pressure. It was thought that this was due to the fact that When such a positive electrode plate is used, large wrinkles (waviness) are generated on the entire positive electrode plate during the production of the wound body in the subsequent step, making it impossible to produce the wound body. That is, it has been difficult to make the bulk density of the positive electrode active material layer to be 2.2 g / cm ³ or more by the room temperature roll pressing.

Therefore, a warm roll press was used to produce a positive electrode plate in which the positive electrode active material layer had a bulk density of about 1.5 to 3.5 g / cm ³ . When a warm roll press was used, some deformation such as generation of small wrinkles was observed when the bulk density of the positive electrode active material layer exceeded 3.0 g / cm ³ , but it will be described later. By using not only tension (tension) but also roller pressing at the time of manufacturing the wound body, it was possible to sufficiently manufacture the battery.

However, the positive electrode active material layer has a bulk density of 3.5.
If it is set to g / cm ³ or more, the deformation of the positive electrode plate is further increased, and even if roller pressing is used at the time of winding, the positive electrode plate becomes wavy and wrinkles occur, making it impossible to produce a wound body. Met. Further, when the microstructure of the positive electrode plate having a bulk density of 3.5 g / cm ³ or more was observed by SEM, the secondary particles of lithium manganate spinel, which is the positive electrode active material, were destroyed and turned into primary particles. Many parts were observed. The secondary particles are such that the primary particles are firmly bonded to each other and are considered to have higher electron conductivity than the simple contact between particles. Therefore, the secondary particles are destroyed to increase the bulk density and to be wound. Even if the body can be manufactured, the effect of reducing the resistance cannot be expected.

The temperature at the time of roll pressing is 80 to
The temperature is preferably 180 ° C., and the temperature of 80 ° C. or higher softens the binder in the positive electrode active material layer, facilitates deformation during pressing, and densifies the positive electrode active material layer, while expanding the positive electrode plate. It becomes easy to suppress the occurrence of deformation and wrinkles. If the temperature is lower than 80 ° C., the softening of the binder may be difficult to occur. Therefore, similarly to the room temperature pressing, there is a limit to increase the bulk density of the positive electrode active material layer. On the other hand, 18
At a high temperature of 0 ° C. or higher, the binder may be melted and deteriorated, and the positive electrode active material layer may be separated from the current collecting substrate and adhere to the roll. is there.

When the roll temperature in the warm roll press is 100 to 150 ° C., the positive electrode plate is less likely to be deformed (elongation, wrinkles, corrugations are generated) and a stable warm roll press treatment is possible. It was Further, the larger the roll diameter, the more the deformation of the positive electrode plate (elongation, wrinkles, and waviness) was suppressed. The roll diameter is preferably 300 mmφ or more, but there is a problem that when the roll diameter becomes large, it may be difficult to machine and achieve shape accuracy. In addition, there is a problem that it becomes difficult to ensure the heat uniformity of the roll when heated, and the deformation such as thermal expansion may increase. Therefore, from this point of view, the roll diameter is 1000 m.
It is preferable to set it to mφ or less. The conditions of the warm roll press described above can be similarly applied to the warm roll press of the negative electrode plate.

Next, the positive electrode plate 6000 after roll pressing
mm and the negative electrode plate 6500 mm were wound with a PP / PE / PP three-layer separator interposed therebetween to produce a wound body. The positive electrode active material layer having a bulk density of less than 3.0 g / cm ³ was wound only with tension. Here, "winding only with tension" means winding a total of four sheets of a positive electrode plate, a negative electrode plate, and a separator (two sheets) around a winding core, and winding each sheet while pulling each sheet. .

On the other hand, the positive electrode active material layer has a bulk density of 3.0 g.
In the case of using a positive electrode plate of / cm ³ or more, a pressure roller was also used while applying tension during winding. As described above, in the positive electrode plate having a positive electrode active material layer having a bulk density of 3.0 g / cm ³ , in most cases, slight deformation such as wrinkles occurs after roll pressing. Even if the tension at the time is increased, the part to which the tension is applied is the uncoated part where the positive electrode active material layer is not formed or has little deformation such as elongation. Therefore, the part where the electrode active material layers face each other. It is difficult to get the tension.

Therefore, a manufacturing method is adopted in which a wound body is manufactured by using a pressure roller in combination so that a tight pressure is applied to a portion where the electrode active materials face each other so that no gap is formed. This makes it possible to manufacture a wound body even when the positive electrode plate is deformed, and it is possible to reflect the effect of resistance reduction by increasing the bulk density of the positive electrode active material layer on the battery characteristics. Became.

Therefore, after manufacturing the wound body as described above, the wound body is inserted into an aluminum case, and EC is used as a solvent.
And DEC in equal volume mixed solvent LiPF6 as electrolyte
Was dissolved to have a concentration of 1 mol / l, a non-aqueous electrolyte solution prepared by injection was injected, and after vacuum impregnation, the battery was sealed by sealing.

Here, when manufacturing the wound body,
The bulk density of the active material layer is different, that is, the total thickness is different.
Since the positive electrode plate is used for the same length,
Lithium manganate has different diameters
If the spinel composition is the same, the initial coating conditions
Are, of course, the same, so of course, coated lithiated manganate
Eum spinel has the same weight. Therefore, the battery capacity
Does not depend on the bulk density of the positive electrode active material layer, and
It was constant, depending only on the composition of um spinel. Immediately
The battery capacity is the above-mentioned lithium manganate spinel.
~ about, : 8.5 Ah, : 8.0 Ah,
: 7.5 Ah, Was 7.5 Ah.

For each battery, a constant voltage charge of 4 A was performed, and then a constant voltage charge of 4.1 V was performed, and then a constant current discharge of 8 A was performed until the battery terminal voltage reached 2.5 V, and the discharge capacity was defined as the battery capacity. . The internal resistance of each battery was calculated from the voltage drop at the start of discharge. That is, the difference between the battery terminal voltage immediately before discharging and during battery rest after charging and immediately after starting discharging (after 1 second in this test) divided by the discharge current of 8 A is the internal resistance of the battery. I decided.

FIG. 3 shows the relationship between the bulk density of the positive electrode active material layer in each battery and the battery internal resistance for each composition of lithium manganate spinel. From FIG. 3, by obtaining the positive electrode active material layer with a bulk density of 2.0 g / cm ³ or more, it is possible to obtain a battery having a low internal resistance stably, that is, with little variation in the characteristics of each battery. It turns out that is possible. When the positive electrode active material layer has a large bulk density, as described above, the volume of the wound body is small even if the battery capacity is the same. Therefore, the battery volume can be downsized and the volume capacity density and volume energy density of the battery can be reduced. It is advantageous in terms. From this point of view, the bulk density of the positive electrode active material layer is preferably 2.5 g / cm ³ or more.

Next, considering the difference in the composition of the lithium manganate spinel, no matter which composition of the lithium manganate spinel is used, when the bulk density of the positive electrode active material layer is 2.0 g / cm ³ or more. It can be seen that a battery having a low internal resistance can be stably obtained. In other words, this result indicates that the resistance characteristics of the battery remarkably reflect the difference in the resistance of the positive electrode plate due to the difference in the bulk density of the positive electrode active material layer. From FIG. 3, the Li / Mn ratio is 0.5.
The if it exceeds, notice that the lower internal resistance is obtained, it can be seen that it is particularly preferable to use lithium manganate was carried out for 2 element substitution.

[0060]

As described above, according to the lithium secondary battery of the present invention, it is possible to provide a lithium secondary battery having a low internal resistance, an excellent large current output characteristic, a large volume energy density, and a constant quality.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic structure of a wound electrode body used in a lithium secondary battery.

FIG. 2 is an explanatory diagram showing a method for producing a wound electrode body using a pressure roller.

FIG. 3 is a graph showing the relationship between the bulk density of the positive electrode active material layer and the internal resistance of the battery.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Winding type electrode body, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5 ... Current collecting tab, 6 ... Winding core, 7 ... Pressure roller.

   ─────────────────────────────────────────────────── ─── Continued front page       (56) Reference JP-A-8-17471 (JP, A)                 Japanese Patent Laid-Open No. 10-261415 (JP, A)                 JP-A-8-69798 (JP, A)                 JP-A-9-171829 (JP, A)                 JP-A-11-111261 (JP, A)                 JP-A-9-306471 (JP, A)                 JP-A-11-120964 (JP, A)                 JP-A-11-273741 (JP, A)

Claims (5)

(57) [Claims] 1. A wound-type electrode formed by winding a positive electrode plate and a negative electrode plate, on each of which a positive electrode active material layer and a negative electrode active material layer are formed on a current collector substrate, around a winding core through a separator. A lithium secondary battery including a body, wherein the positive electrode active material forming the positive electrode active material layer contains lithium (Li) and manganese (Mn) as main components, and Li /
Mn ratio exceeds 0.5, Rutotomoni used lithium manganate having a cubic spinel structure, wherein the positive electrode plate, the bulk density of the positive electrode active material layer is 2 g / cm ³ or more 3.5 g / cm ³ or less And a structure in which the positive electrode active material layer is not formed on at least one end in the width direction of the current collecting substrate and a structure in which current is collected from a plurality of locations , and the length in the winding direction is 1 m or more. Things are used
It becomes Te, and a lithium secondary battery, characterized by the internal resistance is less than 5 m [Omega. 2. The positive electrode active material layer comprises 1 to 10 parts by weight of a carbon fine powder and 1 to 10 parts by weight of an organic substance with respect to 100 parts by weight of the lithium manganate. Rechargeable lithium battery. 3. The lithium secondary battery according to claim 1, wherein highly graphitized carbon fibers are used as the negative electrode active material forming the negative electrode active material layer. 4. The lithium secondary battery according to claim 1, wherein the battery capacity is 2 Ah or more. 5. Use as a power source for an electric vehicle or a hybrid electric vehicle.
The lithium secondary battery according to any one of 1.