Patent Application
20120308863
The present invention relates to small-size wound type batteries in a cylindrical shape or a pin shape, and methods for fabricating the wound type batteries.
In the wound type batteries, such as lithium-ion secondary batteries, a wound body obtained by rolling an electrode group which includes a negative electrode, a positive electrode, a separator, etc., is accommodated in a battery case. In general, the wound body is formed by winding the electrode group around a rod-like winding core, and removing the winding core thereafter.
There are also batteries whose winding core is not removed but used as a negative electrode lead (see Patent Document 1 and Patent Document 2).
In Patent Document 1, a negative electrode pin having an axial core diameter of 1.5 mm is used as a winding core.
In Patent Document 2, a conductive winding core body including a winding core of even smaller diameter, whose maximum outer diameter is in a range of 0.5 mm or more and 3.0 mm or less, is used as a winding core. As the reason why this range of diameter is preferable, Patent Document 2 explains that “if a conductive winding core body made of stainless steel (SUS) is used, and the maximum outer diameter of the winding core body is less than 0.5 mm, the strength of the winding core body is significantly reduced, and an internal short circuit may be easily caused due to damage in the winding core body such as a curve or a crack (paragraph 0031).”
In recent years, as wound type batteries (hereinafter also simply referred to as batteries) are becoming smaller in size, there is a demand for further increase in energy density. To increase the energy density of a small battery, the winding core is preferably as small as possible.
However, the stiffness of the winding core is reduced as the diameter of the winding core is reduced. Thus, it is difficult to wind an electrode group around a small-diameter winding core. For this reason, the winding core needs a certain degree of strength, and practically, the diameter of the winding core cannot be smaller than about 1 mm in terms of stability in mass production.
Even if the diameter of the winding core can be reduced to 1 mm, it is difficult to increase the energy density because a space loss relatively increases as the battery size is reduced. For example, in the case of a battery having a diameter of 18 mm, the space loss due to a winding core (cross-sectional comparison) is 4% or so even if the winding core having a diameter of 3.5 mm is used. However, in the case of a smaller battery having a diameter of about 3.5 mm, the space loss due to a winding core is 8% or more even if the winding core having a diameter of 1 mm is used. This means that the effect of space loss is increased.
In view of this, the objective of the present invention is to provide a wound type battery etc. which can be easily reduced in size and of which the energy density can also be improved.
A battery of the present invention includes a cylindrical battery case having an opening at one end, a sealing member attached to the battery case via an insulating material, for sealing the opening, and a wound body accommodated in the battery case with an electrolyte. The wound body includes a core and an electrode group wound around the core; the electrode group includes a positive electrode plate connected to the sealing member via a positive electrode lead, a negative electrode plate connected to the battery case via a negative electrode lead, and a separator provided between the positive electrode plate and the negative electrode plate.
The core is made of a flexible linear conductor, and functions as the negative electrode lead. For example, a wire may be used as the core.
According to the wound type battery having the above structure, the core is made of a flexible linear conductor, such as a wire. Therefore, the stiffness of the core is insufficient, and the core cannot function as a winding core by itself, unlike winding cores of the conventional batteries of this type.
However, as described later, even a wire etc. can function as a winding core by straining the linear conductor and maintaining the linear conductor in a linear state at the time of winding. Since the diameter of the winding core can be reduced to 1 mm or less, it is possible to reduce the battery in size and improve the energy density.
Moreover, since the core is flexible, it is easy to deform the core. Thus, it is easy to handle the core when the core is used as a negative electrode lead after being used as the winding core. As a result, productivity can be improved.
For example, such a battery can be fabricated by a method including a first step of straining a flexible linear material to maintain the linear material in a strained state in which the linear material is strained by a predetermined tension, and a second step of winding the electrode group around the linear material in the strained state.
According to this fabrication method, the electrode group is wound around the linear material in a strained state. Thus, even a flexible linear material can function as a winding core. Since it is possible to use a linear material whose diameter is smaller than the diameter of conventional materials, the battery can be easily reduced in size, and the energy density can be improved.
Specifically, the second step may include: a first process of fixing the linear material in the strained state to the negative electrode plate orthogonally to a winding direction to form a first connection body having the linear material located at a winding start end of the negative electrode plate; a second process of laying the separator on the first connection body to form a second connection body in which a portion of the first connection body to which the linear material is fixed is connected to the separator; a third process of winding the second connection body around the linear material by rotating the linear material; and a fourth process of placing the positive electrode plate on the second connection body in the middle of the third process to lay the positive electrode plate on the second connection body.
It is preferable to use a linear conductor having electrical conductivity as the linear material. After the second step, a third step of forming the wound body by adjusting a length of an end of the linear conductor to a predetermined length, and a fourth step of inserting the wound body in the battery case, and connecting the end of the linear conductor to an inner surface of the battery case, may be included.
In this case, the linear material may not be removed and used as a negative electrode lead. According to this method, it is possible to prevent the misalignment of the electrode group which tends to occur when the linear material is removed, and possible to reduce the number of fabrication steps because the removal step and an additional step of attaching a current collector lead are not necessary. The number of parts can be advantageously reduced.
For example, it is preferable that a wire is used as the linear conductor, and the linear conductor is connected to the negative electrode plate and the battery case by welding.
According to this method, the electrical connection can be stabler than the electrical connection by adhesion, and the linear conductor can be firmly fixed to the negative electrode plate and the battery case.
A battery etc. of the present invention can be easily reduced in size, and the energy density of the battery can also be improved.
Embodiments of the present invention will be described in detail below based on the drawings. The following embodiments are merely preferred examples in nature, and are not intended to limit the present invention, applications, and use of the invention.
<Wound Type Battery>
The battery case 2 is a press-molded member made of a metal with superior electrical conductivity. The battery case 2 includes a circumferential wall 2a and a bottom wall 2b, and is formed to be in an elongated cylindrical shape having an opening 2c at one end. The battery case 2 functions also as a negative electrode terminal.
The sealing member 3 is positioned in the opening 2c of the battery case 2, and is fixed to the battery case 2 by crimping the circumferential wall 2a. An insulating gasket 5 is interposed between the battery case 2 and the sealing member 3. The sealing member 3 is also made of a metal member with superior electrical conductivity. The sealing member 3 functions as a positive electrode terminal. The opening 2c is closed by the sealing member 3. Thus, the inner space of the battery case 2 is enclosed. The battery case 2 or the sealing member 3 may be provided with a safety valve which is opened when the internal pressure exceeds a predetermined pressure.
In the enclosed inner space of the battery case 2, an electrolyte (not shown) and the wound body 4 are accommodated. In the present embodiment, a nonaqueous organic electrolyte is used as the electrolyte. The wound body 4 is comprised of a core 10, an electrode group 6 wound around the core 10, etc. The electrode group 6 is comprised of a negative electrode plate 20, a positive electrode plate 30, a separator 40, etc.
The core 10 is made of a flexible metal wire (an example linear conductor) which is easily bent, with superior electrical conductivity. The core 10 is also used as a winding core. Thus, as described later, the core 10 is strained strongly to remain in a linear shape. Accordingly, it is preferable that the core 10 has superior tensile strength, and is not much extended by a tension. For example, the core 10 is preferably made of a wire whose modulus of longitudinal elasticity (see the HS specification) is 150 GPa or more. Specifically, piano wires, stainless wires, hard steel wires, etc., may be used as the core 10. Metal wires are advantageous in that they can be welded.
It is preferable that the diameter (the outer diameter) of the core 10 is small. This is because the smaller the diameter of the core 10, the more amount of the electrode group 6 or the electrolyte can be accommodated in the battery case 2. As a result, the energy density can be improved. In the case of the battery 1, the diameter of the core can be reduced to 1 mm, which is a threshold value in the conventional cores, or less. The diameter of the core 10 is preferably in a range of 0.2-0.5 mm in terms of practical use.
The core 10 does not only function as a winding core, but also functions as a negative electrode lead. Specifically, the core 10 is located between the negative electrode plate 20 and the battery case 2 to electrically connect the negative electrode plate 20 and the battery case 2. The arrangement of the core 10 will be described later.
The negative electrode plate 20, the positive electrode plate 30, and the separator 40 are strap-like sheets whose widths are approximately the same. The sheets are layered and rolled to form the electrode group 6. Thus, the negative electrode plate 20 and the positive electrode plate 30 preferably have properties superior in flexibility.
Examples of the material for the negative electrode current collector 21 include a thin film made of copper, stainless steel, nickel, etc. For example, a copper foil can be used as the negative electrode current collector 21. The negative electrode active layer 22 includes a negative electrode active material, a binder, a conductive agent, etc. Examples of the negative electrode active material include black lead, carbon materials such as carbon fiber, silicon compounds such as SiOx etc.
Examples of the binder include polyvinylidene fluoride (PVDF), PVDF derivatives, and rubber-based binders (e.g., fluoro rubber, acrylic rubber, etc.). Examples of the conductive agent include graphites such as black lead, carbon blacks such as acetylene black, etc.
Examples of the material for the positive electrode current collector 31 include a thin film made of aluminum, stainless steel, titanium, etc. The positive electrode active layer 32 includes a positive electrode active material, a binder, a conductive agent, etc. Examples of the positive electrode active material include a lithium-containing composite metal oxide, such as LiCoO2, LiNiO2, LiMnO2, LiCoNiO2, etc. The same materials for the binder and the conductive agent in the negative electrode active layer 22 can be used as the materials for the binder and the conductive agent.
The negative electrode plate 20 is formed by applying a material for the negative electrode active layer 22 in the form of slurry on the surface of the negative electrode current collector 21, and thereafter drying the negative electrode active layer 22 and rolling the negative electrode current collector 21 with the dried negative electrode active layer 22. The positive electrode plate 30 is formed in a similar manner as the negative electrode plate 20.
As shown in
As shown in
The other end of the core 10 (the end closer to the bottom of the battery case 2) has a length that does not obstruct accommodation in the battery case 2. In the present embodiment, this end slightly protrudes from the electrode group 6.
As shown in
The length of the positive electrode plate 30 in the winding direction is shorter than the length of the negative electrode plate 20. As shown in
<Method for Fabricating Wound Type Battery>
As shown in
(First Step)
In the first step P1, a portion to be used as the core 10 (referred to as a core wire 10a) is pulled out from a wire roll 51 as shown in
The both end portions of the core wire 10a are supported by a pair of clamps 53, 53. The core wire 10a is strained until a predetermined tension is applied, and is held by the clamps 53 so that the strained state can be maintained. As a result, the flexible core wire 10a can be maintained in a linear shape, and serve as a winding core. The wire is cut, for example, at a portion indicated by the arrow shown in
(Second Step)
First, in the second step P2, the core wire 10a and the negative electrode plate 20 are connected to each other as shown in
Then, as shown in
The core wire 10a may be connected to the negative electrode current collector 21 after the negative electrode current collector 21 is separated from the negative electrode plate base 52. However, in view of productivity, it is preferable to connect the core wire 10a to the negative electrode current collector 21 before cutting because the negative electrode current collector 21 is a thin film.
In the end of the first process, it is preferable to wind part of the negative electrode current collector 21 around the core wire 10a at low load (a temporary connection process). If the core wire 10a has a small diameter, it results in a small connection area, and the connection strength can be easily reduced. Since tension is applied to the connecting portion during winding, the core wire 10a may be broken or detached from the negative electrode current collector 21, depending on conditions.
To avoid these problems, part of the negative electrode current collector 21 is wound around the core wire 10a a plurality of times at load lighter than the tension applied during winding (i.e., at no load or low load) as shown in
Next, the first connection body 61 and the separator 40 are connected to each other (the second process). Specifically, the separator 40 is prepared and positioned on the first connection body 61 as shown in
The separator 40 is laid on the first connection body 61. The portion of the first connection body 61 to which the core wire 10a is connected is connected to the separator 40 by thermal welding. The thermal welding portion is in the middle of the separator 40 in the longitudinal direction (i.e., the winding direction). Specifically, part of the separator 40 protrudes from the winding start end 20a of the first connection body 61 in a direction opposite to the winding direction.
As a result, a second connection body 62 in which the separator 40 is positioned and fixed to the first connection body 61 is obtained.
Next, as shown in
In the middle of the third process, a positive electrode plate 30 is laid on the second connection body 62 (the fourth process). Specifically, the positive electrode plate 30 is placed on a predetermined portion of the second connection body 62 on the side to which the separator 40 is provided. The core wire 10a is further rotated, with the positive electrode plate 30 placed on the separator 40.
By winding all of the components such as the separator 40, the negative electrode plate 20 and other components are rolled as shown in
(Third Step)
As shown in
Next, as shown in
(Fourth Step)
In the fourth step P4, the wound body 4 is inserted in the battery case 2, and the lead end 11 is connected to the battery case 2. Specifically, as shown in
Then, as indicated by the arrows in
After that, processes such as connecting the positive electrode lead 33 to the sealing member 3, and filling the battery case 2 with an electrolyte are performed. Lastly, the circumferential wall 2a is crimped to fix the sealing member 3 to the battery case 2. As a result, the opening 2c is closed.
A wound type battery etc., according to the present invention is not limited to the above embodiment, and includes various structures other than the structures described in the above embodiment.
For example, the wire used as the core 10 is used also as a negative electrode lead in the fabrication method described in the above embodiment, but the wire used as the core 10 may be removed after the winding of the electrode group 6. The space loss can be reduced in this case, too. Thus, even if a battery is reduced in size, it is possible to improve the energy density.
An example of such a battery is shown in
The present invention may be applied not only to secondary batteries, but also to primary batteries. Materials for the batteries are also not limited to lithium. That is, the present invention can be applied to any batteries in which an electrode group is wound. The linear conductor is not limited to a metal wire. For example, a carbon wire or a composite wire having electrical conductivity may be used.
The connection between the core 10 and the negative electrode plate 20, etc. and the connection between the first connection body 61 and the separator 40 are not limited to welding and thermal welding, but may be adhesion or press fitting, etc. Alternatively, these connections may be achieved by fixing by tape or fixing by lapping (for example, the separator 40 may be folded by 180° to lap around the winding start end 20a of the first connection body 61), etc.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-057549 | Mar 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP11/06736 | 12/1/2011 | WO | 00 | 6/27/2012 |
