JP2000182656A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery having excellent reliability with the drop of the cyclic characteristic suppressed, capable of flattening the resistance distribution in its internal electrode body by locating optimally the collection part to take out the current from a positive electrode plate and a negative electrode plate and capable of stable large current discharging by inducing uniform battery reactions in the internal electrode body. SOLUTION: Besides a non-aqueous electrolytic solution, a lithium secondary battery includes an internal electrode body formed by winding a positive electrode plate 2 and a negative electrode plate 3 on a bobbin with a separator interposed. The current collection part 7 of the positive electrode plate 2 is formed in the range ±30% in longitudinal direction (along the X-axis) of the plate 2 from the center position XA between adjoining current collection parts 8A and 8B formed in the negative electrode plate 3 using as reference the length L between XA and the parts 8A and 8B in the condition that the internal electrode body is spread and the two electrode plates 2 and 3 are overlapped. It may also be accepted that the current collection part 8 of the negative electrode plate 3 is located by reference to the center position between adjoining collection parts 7 of the positive electrode plate 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention flattens the resistance distribution in an internal electrode body of a battery by forming a current collecting portion for extracting current from a positive electrode plate and a negative electrode plate at an appropriate position. The present invention relates to a highly reliable lithium secondary battery that induces a uniform battery reaction in an electrode body, enables stable high-current discharge, and suppresses deterioration in cycle characteristics.

[0002]

2. Description of the Related Art In recent years, lithium secondary batteries have been widely used as power batteries for portable electronic devices such as mobile phones, VTRs, and notebook computers. In addition, since lithium secondary batteries have a high energy density, not only the portable electronic devices but also electric vehicles (eg, electric vehicles, which are being actively spread as low-emission vehicles due to recent environmental problems). It is also attracting attention as a motor drive power supply for EVs or hybrid electric vehicles (HEVs).

An EV battery has a large capacity, a high output, and charge / discharge cycle characteristics (hereinafter, referred to as “cycle characteristics”) in order to obtain predetermined acceleration performance, climbing performance, continuous running performance, and the like.
That. ) Is required. In order to exhibit such characteristics stably, it is important not only to reduce the resistance of the internal electrode body, which is a field of the battery reaction, and the current collecting portion from the internal electrode body, but also to generate a large current. In order to stably obtain the battery, it is necessary to make the battery reaction uniform, suppress local deterioration, and improve cycle characteristics.

Here, as shown in FIG. 4, a wound type internal electrode body which has been studied as an internal electrode body of an EV battery has a structure in which a positive electrode plate 2 and a negative electrode plate 3 are interposed via a separator 4. Each of the electrode plates 2 and 3 (both the positive electrode plate 2 and the negative electrode plate 3; the same applies hereinafter) is wound around the outer periphery of the core 9 and has a positive electrode tab 5 and a negative electrode tab as electrode leads, respectively. 6 is provided.

[0005] The current collecting portion of the internal electrode body 1 is a mounting portion of the tabs 5 and 6 (both the positive electrode tab 5 and the negative electrode tab 6; the same applies hereinafter) in the electrode plates 2.3. However, since the conventional lithium secondary battery was a small battery with a small battery capacity, the area of the electrode plates 2 and 3 was small,
Therefore, it is not always necessary to provide a plurality of current collectors on the electrode plates 2 and 3. In addition, a large current discharge is not normally required for a power supply of a portable electronic device. For this reason, the position where the current collector is provided has not been deeply studied so far.

[0006]

[Problems to be solved by the invention] However, for example,
The HEV is in a mode in which the motor assists the output during acceleration, so that a current of 100 A or more may frequently flow. Further, a current as high as 500 A may flow even for a short time. Here, the internal electrode body 1
When a resistance distribution occurs in the inside, a large current flows intensively in a portion where the resistance is small. In this case, local heat generation and expansion and contraction occur in the electrode plates 2 and 3, causing deterioration and peeling of the electrode active material, thereby deteriorating the cycle characteristics, and the heat generation partially evaporates the electrolytic solution. In addition, the possibility of various problems, such as the rupture of the battery caused by an increase in the battery internal pressure, increases.

Therefore, the inventors have paid attention to the relationship between the position of the current collector in the electrode plates 2 and 3 and the resistance distribution of the electrode plates 2 and 3. When a plurality of current collectors are provided on the positive electrode plate 2, it is considered that the resistance decreases in a region near the current collector and increases near the center of an adjacent current collector. The distribution is the same for the negative electrode plate 3.

[0008] Therefore, as shown in FIG.
At the time of winding 3, the current collector 7 of the positive electrode plate 2 (hereinafter, referred to as “positive electrode current collector 7”) and the current collector 8 of the negative electrode plate 3 (hereinafter, referred to as “negative electrode current collector 8”). When the inner electrode body 1 is deployed and the electrode plates 2 and 3 are overlapped, that is, when the inner electrode body 1 is developed and the electrode plates 2 and 3 are overlapped, the positive electrode current collector 7 and the negative electrode current collector 8 When the electrodes are set so as to be substantially at the same position in the length direction (X-axis direction) of the electrode plates 2 and 3, portions of the electrode plates 2 and 3 having small resistances overlap each other, and at the same time,
Because the parts with large resistance will also overlap,
The result is that the width of the resistance distribution in the internal electrode body 1 increases more and more.

Conventionally, since the resistance of the positive electrode plate 2 is generally higher than the resistance of the negative electrode plate 3, the distribution of the resistance in the internal electrode body 1 is determined by the distribution of the resistance of the positive electrode plate 2. Because of that, this kind of thinking was not done. However, even in such a situation, it is needless to say that it is preferable to reduce the resistance distribution width inside the internal electrode body 1, that is, to flatten the resistance distribution. In addition, recently, since the resistance of the positive electrode active material itself has been reduced and / or the resistance has been reduced by adding a conductive auxiliary agent, the resistance in the internal electrode body 1 which has not been regarded as a problem in the past is considered. It is considered that the distribution greatly affects the charge / discharge characteristics of the battery. In particular, the effects are expected to be extremely large in applications requiring large capacity, high output, and high durability, such as batteries for EVs and HEVs.

[0010]

Means for Solving the Problems The present invention has been made in view of such a problem of the related art, and an object of the present invention is to set a position of a current collecting portion provided on an electrode plate to an internal electrode. By setting the resistance distribution of the body to be flat, a uniform battery reaction in the internal electrode body is induced,
An object of the present invention is to provide a lithium secondary battery that facilitates discharging of a large current and has improved durability and cycle characteristics. That is, according to the present invention, there is provided a lithium secondary battery using an internal electrode body and a non-aqueous electrolyte obtained by winding a positive electrode plate and a negative electrode plate around a winding core with a separator interposed therebetween. When the positive electrode plate and the negative electrode plate are overlapped with each other, the current collector of one of the positive electrode plate and the negative electrode plate is connected to the adjacent collector formed on the other electrode plate. The secondary lithium battery is formed within a range of ± 30% of a length direction of the electrode plate from the center position with reference to a length between the center position of the power unit and the power collection unit. A battery is provided.

[0011] In the lithium secondary battery according to the present invention, the current collector of one electrode plate is connected to the electrode plate (positive plate or positive electrode) from the center position of the adjacent current collector formed on the other electrode plate. It does not matter whether it is the negative electrode plate.) ± 10% in the length direction
It is more preferable that the current collecting portion of one electrode plate is set at the center of an adjacent current collecting portion formed on the other electrode plate. The formation position of the current collector on the electrode plate may be, for example, a current collector of both positive and negative electrodes formed on one end face of the internal electrode body.In the present invention, the positive electrode plate is formed on one end face of the internal electrode body. It is preferable to provide a current collector and a current collector of the negative electrode plate on another end face from the viewpoint of safety, ease of assembly, and the like.

In addition, in the positive electrode plate and the negative electrode plate, there is provided a portion where one current collecting portion is formed for a plurality of winding times, in other words, the wound positive electrode plate or It is preferable that an arbitrary one turn of the negative electrode plate includes one having no current collector.
Such a portion is generally formed so as to appear more on the inner peripheral portion of the internal electrode body.

By the way, there are various methods for forming the current collector. In the present invention, the current collector is formed by welding metal foils as electrode leads to the positive electrode plate and the negative electrode plate, respectively. The method is preferably used. In forming such a current collector, a group of current collectors on the positive electrode plate and a group of current collectors on the negative electrode plate are each formed at an end surface of the internal electrode body within a range of a central angle of 45 °. It is preferable that a group of current collectors be formed on the end face of the internal electrode body and have substantially the same radial diameter. This facilitates bonding of the electrode lead (metal foil) to the terminal, which is preferable. . When the positive electrode plate and the negative electrode plate are unfolded, the interval between the current collectors of the positive electrode plate (hereinafter, referred to as “positive electrode current collector interval”) and the interval between the current collectors of the negative electrode plate (hereinafter, referred to as “negative electrode current collector interval”). ) Is preferably not more than the outer peripheral length of the internal electrode body and not less than ４ of the outer peripheral length. The interval between the positive electrode current collectors and the interval between the negative electrode current collectors are within the above-described range, and are kept substantially constant so as to be within ± 20% of the average value of the intervals between the current collectors. Is preferred.

The present invention is particularly effective when the resistance of the positive electrode plate is small as a whole. Therefore, it is preferable to use lithium manganate as the positive electrode active material. In particular, when the ratio of Li / Mn in the chemical composition is 0.5
It is preferable to use a larger one. Further, the lithium manganate preferably has a cubic spinel structure.

Taking advantage of the excellent output characteristics and durability thus obtained, the lithium secondary battery of the present invention is suitably used as a power source for driving a motor of an electric vehicle or a hybrid electric vehicle. Further, the present invention is suitably applied to a battery having a battery capacity of 2 Ah or more in which the effect of flattening the resistance distribution is remarkably exhibited.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. However, it goes without saying that the present invention is not limited to the following embodiments. The basic configuration of the internal electrode body used in the present invention is the same as that of the internal electrode body 1 previously shown in FIG. FIG. 1 is a plan view showing a schematic configuration of a positive electrode plate 2 and a negative electrode plate 3 used in the lithium secondary battery of the present invention. These are shifted in the width direction, that is, parallel to the Y-axis direction. The positive electrode plate 2 is usually produced by coating the positive electrode active material 14 to a predetermined thickness on both sides of an aluminum foil or a titanium foil as the positive electrode current collector 12, and it is preferable to use an inexpensive aluminum foil from the viewpoint of cost. . The coating of the positive electrode active material 14 is performed by applying a slurry or paste prepared by adding a solvent, a binder, or the like to the positive electrode active material powder to the positive electrode current collector 12 using a roll coater method or the like, and fixing the slurry or paste. Will be

As the positive electrode active material 14, a lithium transition metal composite oxide such as lithium manganate, lithium cobaltate, and lithium nickelate is preferably used. The lower the resistance, the more effectively the resistance distribution in the internal electrode body 1 is flattened, so that lithium manganate having a cubic spinel structure with high electron conductivity (stoichiometric composition: L
It is particularly preferred to use iMn ₂ O ₄ ). Where L
iMn ₂ O ₄ is not limited to those having such a stoichiometric composition, and as long as the crystal structure is maintained, cations are missing or excessive, while oxygen ions are missing. Or it may be present in excess. Further, a part of Mn is converted to another ion such as L.
i, Fe, Mn, Ni, Mg, Zn, B, Al, Co,
Cr, Si, Ti, Sn, P, V, Sb, Nb, Ta,
It may be partially substituted with one or more cations selected from substitution elements M such as Mo and W.

In the present invention, the above-described LiM
Among n ₂ O ₄ , it is particularly preferable to use one having a Li / Mn ratio larger than 0.5, and the internal resistance is further reduced as compared with the case of using a stoichiometric composition. L
Examples of those having an i / Mn ratio greater than 0.5 include Mn
Li (Li _x Mn _2-x ) O ₄ (X
Represents a substitution amount. ) And LiM _X Mn _{2 -X} O _{4 in} which a part of Mn is substituted by the above-mentioned substitution element M other than Li. The former Li / Mn ratio is (1 + X) / (2-
X) and the latter Li / Mn ratio are given by 1 / (2-X), respectively, so that when X> 0, the Li / Mn ratio of both is always greater than 0.5. Preferably, fine carbon powder such as acetylene black is added to the positive electrode active material 14 as a conductive additive.

On the other hand, the negative electrode plate 3 is produced by coating a negative electrode active material 15 on both surfaces of a copper foil or a nickel foil as the negative electrode current collector 13. The manufacturing method is the same as in the case of the positive electrode plate 2 described above. As the negative electrode active material 15, an amorphous carbonaceous material such as soft carbon or hard carbon, or a highly graphitized carbonaceous powder such as artificial graphite or natural graphite is used.

A positive electrode current collector 7 is formed on the positive electrode plate 2 thus manufactured, and a negative electrode current collector 8 is formed on the negative electrode plate 3. The formation of the current collectors 7 and 8 (refers to both the positive electrode current collector 7 and the negative electrode current collector 8; the same applies hereinafter) is performed at any time before, during, or after the positive electrode plate 2 and the negative electrode plate 3 are wound. May be provided. In the present invention, the positive electrode plate 2 and the negative electrode plate 3
By winding tabs 5 and 6 at predetermined positions on each of the positive electrode plate 2 and the negative electrode plate 3 by means of ultrasonic welding or the like while winding them through the separator 4 so as not to contact with each other, the current collecting unit The method of forming 7.8 is suitably adopted.

Here, the separator 4 has a three-layer structure in which a lithium-ion permeable polyethylene film (PE film) having micropores is sandwiched between porous lithium-ion permeable polypropylene films (PP films). Are preferably used. This is because when the temperature of the internal electrode body rises, the PE film
It also softens at 30 ° C., crushes the micropores, and also serves as a safety mechanism for suppressing the movement of lithium ions, that is, the battery reaction. By sandwiching the PE film between PP films having a higher softening temperature, even when the PE film is softened, the PP film retains its shape and prevents contact and short circuit between the positive electrode plate 2 and the negative electrode plate 3. In addition, it is possible to reliably suppress the battery reaction and ensure the safety.

Now, the current collectors 7 and 8 in the present invention
When the internal electrode body 1 is unfolded and the positive electrode plate 2 and the negative electrode plate 3 are overlapped, the current collector of one of the positive electrode plate 2 and the negative electrode plate 3 is placed adjacent to the other electrode plate. With reference to the length between the central position of the matching current collector and the current collector, from this central position ± 30 in the length direction of the electrode plates 2 and 3
%. For example, the length of the negative electrode plate 3 from the center position of the positive current collector 7 is determined based on the length between the central position of the adjacent current collector 8 formed on the negative electrode plate 3 and the current collector 8. The direction is formed within a range of ± 30%.

This will be described with reference to FIG. 1. First, when considering the formation positions of the current collectors 7 and 8,
It is necessary to consider based on either one of the current collectors 7 and 8 (current collector interval). Therefore, in this embodiment,
The interval between the negative electrode current collectors 8 (the interval between the negative electrode current collectors) is considered as a reference. However, it is obvious that the interval between the positive electrode current collectors 7 (the interval between the positive electrode current collectors) may be used as a reference.

In FIG. 1, a central position between any adjacent negative electrode current collectors 8 A and 8 B in the negative electrode current collector 8 is denoted by XA, and the center position XA and the negative electrode current collector 8 A or the negative electrode current collector 8 B
Is defined as a reference distance L. At this time, one positive electrode current collector 7A on the positive electrode plate 2 is set to have a length of L × (± 0.3) in the length direction of the negative electrode plate 3 with respect to the center position XA, that is, in both the positive and negative directions of the X axis. Within the range D.

When the positive current collector 7 is formed within the range D determined by the position where the negative current collector 8 is formed, the low-resistance portion of the positive electrode plate 2 and the high-resistance portion of the negative electrode plate 3 overlap with each other, Conversely, since the high-resistance portion of the positive electrode plate 2 and the low-resistance portion of the negative electrode plate 3 overlap, the resistance distribution in the internal electrode body is flattened. As a result, the current distribution in the internal electrode body is made uniform, and it is possible to avoid current concentration on a part of the internal electrode body 1 which is likely to occur particularly when a large current is discharged.

In consideration of such effects, the positive electrode current collector 7 A is located at the center position XA, which is a narrower range within the range D.
Is more preferably formed within the range of L × (± 0.1) in the X-axis direction, and the most preferable state is when the positive electrode current collector 7A is located at the center position XA. In FIG. 1, the negative electrode current collectors 8 are formed at regular intervals, that is, the intervals between the negative electrode current collectors are constant so that the current collection areas handled by the tabs 6 are equal. The electric parts 7 are also formed at equal intervals. Thus, making the current flowing through the tabs 5 and 6 substantially constant also contributes to the uniformity of the current distribution in the internal electrode body 1. However,
As will be described later, the case where the interval between the positive electrode current collectors and / or the interval between the negative electrode current collectors are not completely constant within a range in which the productivity is considered and the battery characteristics are maintained is also allowed.

Note that the above-described condition regarding the formation position of the current collector must be satisfied for all the selected adjacent current collectors. For example, when five current collectors are provided on the negative electrode plate, the central position between adjacent negative electrode current collectors is four. Therefore, it is necessary to provide the positive electrode current collectors within a certain distance range from the central position in all of the four central positions. This is because if the positive current collector is provided in any one of the four central positions outside the above range, the resistance distribution width becomes large in that part, and the current density distribution becomes large. The result is that it is not preferable.

Incidentally, since the electron conductivity of the positive electrode active material 14 is generally smaller than the electron conductivity of the negative electrode active material 15, the resistance distribution of the internal electrode body 1 is the same as the resistance distribution of the positive electrode plate 2 having a large resistance itself. Influence becomes dominant. Conversely, this suggests that as the resistance of the positive electrode plate 2 decreases, the effect of flattening the resistance distribution caused by the formation positions of the current collectors 7 and 8 described above increases. Therefore, in the present invention, a positive electrode plate 2 having a small resistance is obtained.
It is preferable to use the above-described various LiMn ₂ O ₄ as the positive electrode active material 14.

In forming the current collecting portion, for example, a current collecting portion having both positive and negative electrodes may be formed on one end surface of the internal electrode body. In this case, the contact between the tabs of the positive and negative electrodes may be formed. In addition to the danger, when providing the positive and negative electrode terminals of the battery on the battery end face respectively, the battery case is used as a current path,
Alternatively, there arises a problem that it is necessary to separately form a current path. Therefore, it is preferable that a current collector of the positive electrode plate is provided on one end face of the internal electrode body and a current collector of the negative electrode plate is provided on another end face, and electrode terminals are provided on the battery end faces on each end face side. That is, in FIG. 1, it is possible to use the internal electrode body produced by winding the positive electrode plate 2 and the negative electrode plate 3 in a state of being overlapped only by parallel movement in the Y-axis direction. It is preferable from the point of view.

According to the above description, the current collecting portion refers to the position where the tab is attached, but the form of forming the current collecting portion is not limited to the formation of the tab by welding. For example, if the current collector is formed within the above-described predetermined range and the current collectors of the positive and negative poles are cut out to provide a portion corresponding to a tab, the base of that portion is provided. Can be regarded as a current collector. Further, the shape of the tab is not limited to the rectangular shape shown in FIG. 1, and various shapes can be used. Even if the material is a linear material other than the foil, there is no problem. Furthermore, the tab does not have to be welded only once to one current collector,
The current collecting portion may be provided by welding a plurality of tabs within the range D.

Next, without deteriorating the battery characteristics,
The conditions for forming the current collector for simplifying the battery assembling operation will be described. As described above, it is preferable in terms of battery characteristics that the intervals between the positive electrode current collectors and / or the intervals between the negative electrode current collectors be equal, but the inner and outer peripheral portions of the internal electrode body 1 have a circumference per turn. Vary greatly in length. Therefore,
If the structure is such that at least one current collecting portion is provided for each winding while keeping the current collecting portion interval constant, the current collecting portion interval is determined by the length of the innermost circumference, and the current collecting portion to be formed is formed. The number is enormous, and there is a problem that the workability at the time of attaching the tab to a current terminal or the like for extracting a current to the outside of the battery is reduced. On the other hand, without keeping the current collector interval almost constant,
In a configuration in which at least one current collecting portion is present per one turn, the current collecting resistance is reduced at the inner peripheral portion of the internal electrode body, so that when a large current flows, current concentrates on the inner peripheral portion. As a result, the deterioration of the electrode active material is promoted, and the cycle characteristics deteriorate.

Therefore, in order to avoid such a problem, in the present invention, there should be a portion where one current collecting portion is formed for a plurality of winding times, in other words, , Wound positive electrode plate 2 or negative electrode plate 3
It is preferable to set the current collector interval so that there is a portion where the current collectors 7 and 8 are not formed in any one of the turns. Such portions naturally appear in the inner peripheral portion of the internal electrode body 1.

However, even if this condition is satisfied, the problem is that the current collectors are formed at random positions on the end face of the internal electrode body if the current collector intervals are formed to be constant. Is left. In this case, it is not only difficult to join the tab to the current terminal or the like, but also depending on the connection position with the current terminal, the tab may be damaged due to the torsion stress being applied to the tab and the tab being cut. is there.

Therefore, while the current collector is formed in accordance with the above-described conditions, more preferably, one group of the positive electrode current collector 7 and one group of the negative electrode current collector 8 are each formed at the center angle at the end face of the internal electrode body 1. Preferably, it is formed within a range of 45 °. This state is shown in a plan view of the internal electrode body of FIG. 2 viewed from the end face. The positive electrode current collector 7 is formed such that the center of the positive electrode current collector 7 is located in the region A in FIG. In this case, the negative electrode current collector 8 is formed in a region B that is point-symmetric with the region A about the center of the internal electrode body 1. Note that it has already been described that the region A and the region B are preferably formed on different end faces of the internal electrode body 1 respectively. Considering this central angle theoretically, it is possible to provide eight regions for each electrode plate. However, considering the workability of assembling the battery, it is preferable that the number be four or less.

Further, each group of the current collectors 7 and 8 includes:
When formed on the end face of the internal electrode body 1 within the above-described region of the central angle of 45 ° and substantially on the same moving radius, that is, on the straight line in the radial direction, it is easier to join the tab to the current terminal. Thus, the productivity is improved, and the torsional stress applied to the tab is reduced, so that breakage of the tab is effectively avoided, which is preferable. One embodiment of this state is shown in FIG. In contrast to the current collectors 7 formed so as to be substantially aligned, the current collectors 8 are similarly formed so as to be substantially aligned at a position symmetrical with respect to the center of the core 9. Note that such a restriction on the formation positions of the positive electrode current collector 7 and the negative electrode current collector 8 is suitably used when the tabs 5 and 6 are collectively connected to a current terminal or the like at one location for each region.

The interval between the positive electrode current collector and the interval between the negative electrode current collectors is preferably equal to or less than the outer peripheral length of the internal electrode body 1 and equal to or more than ４ of the outer peripheral length. As described above, it is preferable that the positions where the current collectors 7 and 8 are formed be set so as to be substantially on the same radius. Here, the larger the number of the current collectors 7 and 8, the smaller the current collection resistance. Is obvious,
The current collecting unit intervals are set such that the other current collecting unit intervals are equal to this reference interval as much as possible with respect to the outermost peripheral current collecting unit intervals, and the positions of the current collecting units are substantially on the same radius. It is desirable to line up.

The intervals between the positive electrode current collectors and the intervals between the negative electrode current collectors are assumed to be substantially constant so as to be within ± 20% of the average of the intervals between the positive electrode current collectors and the negative electrode current collectors, respectively. This is preferable because it does not cause deterioration in cycle characteristics.

The lithium secondary battery of the present invention in which the internal electrode body having such a structure and in which the resistance distribution is flattened is accommodated in a battery case and filled with a non-aqueous electrolyte, has a uniform battery reaction. It has excellent output characteristics and durability due to the induction of, and is suitably used as a power supply for driving a motor of an electric vehicle or a hybrid electric vehicle. Further, the present invention is suitably applied to a battery having a battery capacity of 2 Ah or more in which the effect of flattening the resistance distribution is remarkably exhibited.

As the non-aqueous electrolyte, ethylene carbonate (EC), diethyl carbonate (DE)
C), carbonates such as dimethyl carbonate (DMC), propylene carbonate (PC) and γ
- butyrolactone, dissolved in tetrahydrofuran, alone or a mixed solvent of an organic solvent such as acetonitrile, lithium complex fluorine compound such as LiPF ₆ and LiBF ₄ as an electrolyte, or one or two or more kinds of LiClO ₄ lithium halides such as The used non-aqueous electrolyte is suitably used.

[0040]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Preparation of Battery) Li having a stoichiometric composition
Mn ₂ O ₄ spinel (Li / Mn ratio = 0.5) was used as a positive electrode active material, and a carbon powder (acetylene black) for improving conductivity was added thereto and mixed, and the mixture was applied to an aluminum foil. Surface shape is winding direction length 3400
A positive electrode plate 2 having a size of 200 mm × width 200 mm was prepared. On the other hand, the negative electrode plate 3 is formed by applying a highly graphitized carbon material (fibrous powder) to a copper foil, so that the length in the winding direction is 3600 mm × 200 mm in width.
Was prepared. The positive electrode plate 2 and the negative electrode plate 3 thus manufactured were wound while being insulated using a microporous separator 4 made of polypropylene to prepare an internal electrode body.

It is to be noted that, at the time of this winding, the positional relationship shown in FIG.
The tabs 5 and 6 were attached to predetermined positions of the electrode plates 2 and 3 by ultrasonic welding so that the current collectors 7 and 8 were formed so that the positive electrode current collector 7 was formed substantially at the center position. Here, aluminum was used for the tab 5 for the positive electrode, and copper foil was used for the tab 6 for the negative electrode. The current collectors are spaced at intervals of about 100 mm so as not to be longer than the circumferential length of the battery, and the current collectors 7 and 8 have the end faces of the internal electrode body 1 after being wound so as to have the structure shown in FIG. It was set so as to be lined up on almost the same moving radius.
Thirty tabs were used, and one tab is provided for a plurality of turns in the inner peripheral portion.

Next, a battery 50 having the battery structure shown in FIG. 6 was manufactured. First, the tab 5 of the produced internal electrode body 1
6 is a positive internal terminal 74A and a negative internal terminal 74, respectively.
The rivet used as B was collectively connected at one place by caulking. Here, the positive electrode internal terminal 74A is a rivet made of aluminum, and is joined to the positive electrode lid 71A made of the same aluminum. In addition, the positive electrode lid 7
A female screw-shaped positive external terminal 73A also made of aluminum is bonded to the surface opposite to the surface to which the positive internal terminal 74A of 1A is bonded. The positive external terminal 73
An electrolyte injection port 77 is provided below A in such a manner as to penetrate the positive electrode cover 71A.

The structure on the negative electrode side is the same as that on the positive electrode side, and a copper member is used for all of the negative electrode internal terminal 74 B, the negative electrode cover 71 B, and the externally threaded negative electrode external terminal 73 B. However, the electrolyte inlet 77 is not provided in the negative electrode lid 71B.

Thus, the positive and negative internal terminals 74 A
The inner electrode body 1 to which 74B or the like has been attached has an outer diameter of 50 mm.
After being inserted into an aluminum cylindrical battery case 72 having a diameter of φ, a thickness of 1 mm, and a length of 245 mm, drawing was performed near both ends of the internal electrode body 1 to form a projection 81 on the battery case 72. Furthermore, a sealing material 8 made of an insulating material
2 and a battery case 72 and positive and negative electrode lids 71A and 71
Both ends of the battery case were sealed by caulking so that B did not conduct. Note that an insulating polymer film 79 was disposed between the internal electrode body 1 and the inner peripheral surface of the battery case 72.

Subsequently, the battery 50 is placed under a reduced pressure atmosphere with the electrolyte injection port 77 facing upward, and the electrolyte injection port 7 is
The electrolyte injection nozzle was inserted into the bottom of the battery so as to penetrate through the hollow portion of the core 7 and the winding core 9, and a predetermined amount of the electrolyte was injected to sufficiently impregnate the internal electrode body 1. Thereafter, an unnecessary electrolyte was discharged with an electrolyte injection nozzle in an inert gas atmosphere, and the electrolyte injection port 77 was sealed with a screw.
The electrolyte was LiPF ₆ electrolyte of EC and DE.
The solution dissolved in a mixed solution of the same amount of C was used. The battery manufactured by the above steps is referred to as the battery of Example 1.

On the other hand, Li / M
A battery of Example 2 was manufactured using LiMn ₂ O ₄ spinel having an n ratio of 0.55 and the other conditions were the same as in Example 1 described above. The production process of the batteries of Comparative Examples 1 and 2 is the same as that of the batteries of Examples 1 and 2, but the positions of the current collectors 7 and 8 on the positive electrode plate 2 and the negative electrode plate 3 are shown in FIG. As a result, a battery was prepared in which the positions were substantially the same in the winding direction. In the battery of Comparative Example 1, a LiMn ₂ O ₄ spinel having a Li / Mn ratio of 0.5 was used as the positive electrode active material.
A 0.55 LiMn ₂ O ₄ spinel was used. Then, the manufactured batteries of the example and the comparative example were fully charged by 10 A constant current-4.1 V constant voltage charging. The battery capacity at full charge was 25 for the batteries of Example 1 and Comparative Example 1.
Ah, 22 Ah for the batteries of Example 2 and Comparative Example 2.
Met.

(Evaluation of Cycle Characteristics) The cycle characteristics of the batteries of Example 1 and Comparative Example 1 were evaluated by repeating the charge / discharge cycle shown in FIG. In one cycle, the battery in a 50% charged state was discharged at a current of 250 C corresponding to 10 C (discharge rate) for 9 seconds, paused for 18 seconds, charged at 175 A for 6 seconds, subsequently charged at 45 A for 27 seconds, and then again. 5
The pattern was set to a 0% charged state. By finely adjusting the current value of the second charge (45 A),
The DOD shift in each cycle was kept to a minimum. In order to know the change in the battery capacity during the endurance test, the capacity was measured at a current intensity of 0.2 C at a charge stop voltage of 4.1 V and a discharge stop voltage of 2.5 V. The rate of change of the discharge capacity was determined from the value obtained by dividing the discharge capacity at the first time by the first discharge capacity. The cycle characteristics of the batteries of Example 2 and Comparative Example 2 were also evaluated by the same method.
In consideration of the battery capacity, the sizes were all 22/25 times.

(Test Results) The test results are shown in FIG. When the internal electrode body is expanded, the discharge capacity of the batteries of Examples 1 and 2 in which the positive electrode current collector is formed substantially at the center of the adjacent negative electrode current collector is suppressed. This is because, in the batteries of Examples 1 and 2, the current distribution hardly occurs in the internal electrodes because the resistance distribution in the internal electrodes is flattened.
It is considered that this is largely due to the fact that a uniform battery reaction was induced, so that a load was applied to some of the electrode active materials and deterioration was prevented from progressing.

It is to be noted that a decrease in the discharge capacity of Example 2 using the LiMn ₂ O ₄ spinel having a Li / Mn ratio larger than 0.5 is suppressed. This is because the internal resistance of the battery of Example 2 was smaller than the internal resistance of the battery of Example 1, so that in the battery of Example 2, the resistance itself of the positive electrode plate was reduced, and It is considered that the distribution width approaches the resistance distribution width of the negative electrode plate, and as a result, the effect of flattening the resistance distribution of the internal electrode body is remarkably exhibited.

On the other hand, in the batteries of Comparative Examples 1 and 2, since the resistance distribution in the internal electrode body is large, a large current easily flows in a portion where the current collecting portion having a small resistance is formed. It is considered that the deterioration of the electrode active material due to the large current progressed, and the cycle characteristics decreased. In addition,
The difference in the rate of decrease in the discharge capacity between Comparative Example 1 and Comparative Example 2 is considered to be due to the same cause as the difference in the rate of change in the discharge capacity between Example 1 and Example 2 described above. That is, Li / M
It is considered that when LiMn ₂ O ₄ spinel having an n-ratio larger than 0.5 was used, the internal resistance itself of the battery was reduced, so that current concentration hardly occurred, and a decrease in discharge capacity was suppressed. Can be

[0052]

As described above, according to the lithium secondary battery of the present invention, the formation position of the current collector is optimized so that the resistance distribution in the internal electrode body is flattened. In this case, a remarkable effect is obtained in that a battery reaction is uniformly induced, thereby obtaining a battery having excellent output characteristics, in particular, capable of stably discharging a large current. In addition, since a current is prevented from being concentrated on a specific portion in the internal electrode body, there is a remarkable effect that partial deterioration of the electrode active material is suppressed and cycle characteristics are improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a formation position of a current collector in an electrode plate suitably used in the present invention.

FIG. 2 is a cross-sectional view showing one embodiment of a structure of a battery end face suitably adopted for a lithium secondary battery of the present invention.

FIG. 3 is a cross-sectional view showing another embodiment of the structure of the battery end face suitably employed in the lithium secondary battery of the present invention.

FIG. 4 is a perspective view showing a general structure of an internal electrode body.

FIG. 5 is a plan view showing an example of an arrangement of a current collecting portion of an electrode plate in a state where a conventional wound internal electrode body is developed.

FIG. 6 is a cross-sectional view showing one embodiment of a battery structure suitably adopted for the lithium secondary battery of the present invention.

FIG. 7 is an explanatory diagram showing a charge / discharge pattern in a cycle test.

FIG. 8 is a graph showing the results of a cycle test.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Internal electrode body, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5 ... Positive electrode tab, 6 ... Negative electrode tab, 7 ... Positive current collector, 8 ... Negative electrode current collector, 9 ... Core , 12 ... positive electrode current collector, 1
3: negative electrode current collector, 14: positive electrode active material, 15: negative electrode active material, 50: battery, 71A: positive electrode cover, 71B: negative electrode cover, 7
2 ... Battery case, 73A ... Positive electrode external terminal, 73B ... Negative electrode external terminal, 74A ... Positive electrode internal terminal, 74B ... Negative electrode internal terminal, 77 ... Electrolyte injection port, 79 ... Insulating film, 81 ...
Projecting portion, 82: sealing material.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (14)

[Claims] 1. A lithium secondary battery using a non-aqueous electrolyte and an internal electrode body obtained by winding a positive electrode plate and a negative electrode plate around a winding core via a separator, wherein the internal electrode body is developed. Then, in a state where the positive electrode plate and the negative electrode plate are overlapped, the current collector of one of the electrode plates of the positive electrode plate or the negative electrode plate is a current collector of an adjacent current collector formed on the other electrode plate. A lithium secondary battery formed within a range of ± 30% of the length of the electrode plate from the center position with reference to the length between the center position and the current collector. 2. The current collector of one of the positive electrode plate and the negative electrode plate is located between a center position of an adjacent current collector formed on the other electrode plate and the current collector. 2. The lithium secondary battery according to claim 1, wherein the electrode is formed within a range of ± 10% of the length of the electrode plate from the center position with respect to the length of the electrode plate. 3. The current collector of the positive electrode plate is provided on one end face of the internal electrode body, and the current collector of the negative electrode plate is provided on another end face. 2. The lithium secondary battery according to 2. 4. The positive electrode plate and the negative electrode plate each include a portion where one current collecting portion is formed for a plurality of turns. Item 7. The lithium secondary battery according to Item 1. 5. The current collector according to claim 1, wherein the current collector is formed by welding a metal foil as an electrode lead to the positive electrode plate and the negative electrode plate. The lithium secondary battery according to the above. 6. A group of current collectors on the negative electrode plate and a group of current collectors on the positive electrode plate are each formed within a range of a central angle of 45 ° on an end face of the internal electrode body. The lithium secondary battery according to claim 1. 7. The lithium secondary battery according to claim 6, wherein the group of current collectors is formed on the end face of the internal electrode body with substantially the same radius. 8. The distance between the positive electrode current collector and the distance between the negative electrode current collectors is
The lithium secondary battery according to claim 6, wherein the length is equal to or less than the outer peripheral length of the internal electrode body and equal to or more than ４ of the outer peripheral length. 9. The interval between the positive electrode current collector and the interval between the negative electrode current collectors is as follows:
The lithium secondary battery according to any one of claims 6 to 8, wherein each of the distances is within ± 20% of an average value of the interval between the positive electrode current collector and the interval between the negative electrode current collectors. 10. The lithium secondary battery according to claim 1, wherein lithium manganate is used as the positive electrode active material. 11. Li in the lithium manganate
The lithium secondary battery according to claim 10, wherein the ratio of / Mn is larger than 0.5. 12. The lithium manganate according to claim 10, wherein the lithium manganate has a cubic spinel structure.
2. The lithium secondary battery according to 1. 13. The lithium secondary battery according to claim 1, which is used as a power supply for driving a motor of an electric vehicle or a hybrid electric vehicle. 14. The lithium secondary battery according to claim 1, having a battery capacity of 2 Ah or more.