JP5707295B2 - Square non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery having a rectangular container.

  In non-aqueous electrolyte secondary batteries, ensuring safety is an important issue. In particular, when an overcharge occurs, an unsafe phenomenon accompanied by a sudden increase in internal pressure or temperature may occur, which may lead to the rupture of the battery container. Various measures have been taken to avoid such a phenomenon. . Various methods have been proposed as means for preventing unsafe phenomena due to overcharging. For example, a method for preventing overcharging itself by a protection circuit, a method for providing a mechanism for interrupting a current circuit by utilizing an increase in internal pressure due to overcharging as disclosed in Patent Document 1, and a patent As disclosed in Document 2, countermeasures such as a method of causing a soft short (making a short-circuit state with a certain resistance) by utilizing deformation of the wound group have been proposed.

Japanese Patent No. 4590856 Japanese Patent Laid-Open No. 11-73941

  A method of preventing overcharge by a control circuit such as a protection circuit has a risk in the case of a circuit failure or the like. For this reason, if safety is ensured by the structure of the battery, an inherently safe battery system can be obtained.

  The present invention prevents an unsafe phenomenon (for example, rupture of a battery container) that can occur when an internal pressure increases due to overcharging in a nonaqueous electrolyte secondary battery having a rectangular container, and improves safety. With the goal.

  In response to the above problems, the rectangular nonaqueous electrolyte secondary battery according to the present invention has the following characteristics. A prismatic non-aqueous electrolyte secondary battery having a wound group in which a positive electrode and a negative electrode are wound flatly through a separator, and a battery container storing the wound group, wherein the wound group includes: The battery container has a flat portion that forms a flat shape and a curved portion, and the battery container has a protrusion on an inner wall facing the curved portion of the wound group.

  The prismatic nonaqueous electrolyte secondary battery according to the present invention can prevent unsafe phenomena such as rupture of a battery container, which can occur when the internal pressure increases due to overcharging, and can improve safety. .

It is an external appearance perspective view of the square nonaqueous electrolyte secondary battery in a present Example. It is a cutting schematic diagram which shows the structure of the winding group accommodated in the inside of the square nonaqueous electrolyte secondary battery in a present Example, and a current collection component. It is a cross-sectional view of the battery container of the square nonaqueous electrolyte secondary battery in the present example. FIG. 4 is a cross-sectional view of a rectangular nonaqueous electrolyte secondary battery taken along line A-A ′ in FIG. 3. It is a schematic diagram which shows a mode that a battery container expand | swells in the width direction when it expand | swells in the thickness direction. It is a schematic diagram which shows the state which the battery container contracted in the width direction and the projection part was pushed in the winding group. FIG. 4 is a cross-sectional view of the prismatic nonaqueous electrolyte secondary battery taken along line A-A ′ in FIG. 3, and is a diagram in the case where protrusions are scattered in the height direction. FIG. 4 is a cross-sectional view of the prismatic nonaqueous electrolyte secondary battery taken along line A-A ′ in FIG. 3, and is a view when a protrusion is divided into three in the height direction.

  Examples of the prismatic nonaqueous electrolyte secondary battery according to the present invention will be described. In this example, an example in which a lithium ion battery is used as a nonaqueous electrolyte secondary battery will be described. However, application of the present invention is not limited to non-aqueous electrolyte secondary batteries other than lithium ion batteries.

  There are various types of exterior shapes of lithium ion batteries, which are one type of non-aqueous electrolyte secondary battery, but in recent years, a rectangular shape is often used from the viewpoint of mounting on a device. This embodiment improves the safety of such a rectangular lithium ion battery. In this embodiment, an oval square battery (flat rectangular battery) having a cross-sectional shape will be described. Needless to say, the application of the present invention is not limited to various square batteries similar to the above.

  FIG. 1 is an external perspective view of a prismatic nonaqueous electrolyte secondary battery in the present embodiment. A prismatic battery 100 has an exterior shape as shown in FIG. 1, and includes a positive electrode terminal 1, a negative electrode terminal 2, a gas release valve 3, and a liquid injection port 4 in a battery container 5 having an oval cross-sectional shape. . The positive electrode terminal 1 and the negative electrode terminal 2 are terminals for electrical connection to the outside, and the gas release valve 3 discharges gas generated inside when there is an abnormality such as overcharge. The electrolytic solution is injected into the battery container 5 from the injection port 4. The positive electrode terminal 1, the gas release valve 3, and the liquid injection port 4 are provided on the upper lid plate, and the negative electrode terminal 2 is provided on the bottom lid plate.

  In the following description, the longitudinal direction of the cross-sectional shape (oval shape) of the battery case 5 is referred to as the “width direction”, the short direction is referred to as the “thickness direction”, and the direction orthogonal to the width direction and the thickness direction is referred to. This is called “height direction”. In FIG. 1, the height direction is a direction connecting the positive electrode terminal 1 and the negative electrode terminal 2 of the battery container 5. The winding group described later will also be described using these directions.

  FIG. 2 is a schematic cutaway view showing the structure of the winding group and the current collecting component housed in the rectangular nonaqueous electrolyte secondary battery in the present embodiment. As shown in FIG. 2, the prismatic battery 100 houses a wound group 6 that is a power generation element inside a battery container 5. The wound group 6 is electrically connected to external terminals (the positive terminal 1 and the negative terminal 2) via the current collecting component 7. In FIG. 2, the current collecting component connected to the negative electrode terminal 2 is not shown.

  The wound group 6 is produced by winding a positive electrode and a negative electrode around a plate-like axis with a separator made of a polyethylene microporous film interposed therebetween. As shown in FIG. 2, the wound group 6 has a flat shape, and includes a flat surface portion 6 a formed of a flat surface and a curved portion 6 b formed of a curved surface. The wound group 6 includes two flat portions 6a and two curved portions 6b. As can be seen from FIG. 2, the winding axis direction of the winding group 6 is parallel to the height direction.

The positive electrode comprises 85 parts by weight of a lithium-containing composite oxide represented by the chemical formula LiCoO ₂ , 10 parts by weight of a conductive material made of carbon black and graphite, and 5 parts by weight of a polyvinylidene fluoride resin. It is prepared by dissolving in NMP (N-methyl-2-pyrrolidone solution) to obtain a uniform slurry, drying the slurry applied to an aluminum foil, and press-molding the slurry to a predetermined thickness.

  The negative electrode was prepared by dissolving 90 parts by weight of graphite, 5 parts by weight of a carbon black conductive material, and 5 parts by weight of a polyvinylidene fluoride resin binder in NMP to form a uniform slurry. It is produced by drying a material applied to a copper foil and press-molding it to a predetermined thickness.

  Each of the positive aluminum foil and the negative copper foil is provided with a portion where no slurry is applied to one end in the height direction. By welding the portion not coated with this slurry to the current collecting component 7, the positive electrode and the positive electrode terminal 1 and the negative electrode and the negative electrode terminal 2 are electrically connected.

  FIG. 3 is a cross-sectional view of the battery container of the rectangular nonaqueous electrolyte secondary battery in the present example. In the present embodiment, the battery container 5 has a protruding portion 8 that protrudes toward the winding group 6 on the inner wall that faces the curved portion 6 b when the winding group 6 is stored. The protrusion 8 has a cross-sectional shape perpendicular to the height direction, that is, a bar shape whose cross-sectional shape is a semicircular shape, and extends in the height direction. However, in this cross-sectional shape, the semicircular diameter portion is formed by a curve having a curvature in accordance with the shape of the inner wall of the battery case 5. In the present embodiment, when the battery case 5 is not deformed, the protruding portion 8 contacts the curved portion 6b of the wound group 6 without stress.

  The protruding portion 8 is formed by welding a wire rod made of the same material as the battery case 5 and having a cross-sectional shape cast into the above-described semicircular shape to the inner wall of the battery case 5. Specifically, this wire can be welded to the inner wall of the battery container 5 in several spots with a YAG laser to form the protrusion 8.

  In this embodiment, the projecting portion 8 has a semicircular cross-sectional shape, but is not limited thereto. The cross-sectional shape of the protrusion 8 can be various shapes such as a rectangle and a triangle. As will be described later, the cross-sectional shape of the protrusion 8 can be a control factor for the soft short between the positive electrode and the negative electrode.

  In FIG. 3, the protrusion 8 is formed on two inner walls (inner walls at both ends in the width direction) of the inner wall of the battery container 5 that are opposed to the two curved portions 6 b of the wound group 6. . The protrusion 8 may be formed only on the inner wall (the inner wall at one end in the width direction) at one of the two positions.

  FIG. 4 is a cross-sectional view of the rectangular nonaqueous electrolyte secondary battery taken along line A-A ′ in FIG. 3. As shown in FIG. 4, the protrusion 8 in this embodiment is divided into two near the center in the height direction and is discontinuous in the height direction. In addition, the section where the protruding portion 8 exists in the height direction is longer than the section where the wound group 6 exists. As described above, the protrusion 8 is a rod having a semicircular cross-sectional shape, and the vertical cross-sectional shape is rectangular as shown in FIG.

  When the battery container 5 receives a force that expands in the thickness direction and contracts in the width direction, the protrusion 8 is pressed against the winding group 6. At this time, since the protrusion 8 has a longer section in the height direction than the wound group 6, in the wound group 6, the protrusion 8 is pushed even at the end in the height direction.

  Thus, the protrusion 8 strongly presses the wound group 6 and finely cuts the separator. And since a positive electrode and a negative electrode contact via the protrusion part 8, a soft short is induced. By this soft short, the positive electrode and the negative electrode are short-circuited by a small area, and it is possible to avoid an unsafe phenomenon by releasing electric energy in a state where the energization resistance is large (that is, with a small short-circuit current). .

  Since the protrusion 8 has a longer section in the height direction than the wound group 6, a soft short is induced by the presence of a protrusion at the end of the wound group 6 where the protrusion is pushed with a smaller stress. It has become easier. In addition, since the protrusion 8 is divided into two near the center in the height direction and is discontinuous, the end of the protrusion 8 near the center in the height direction is likely to be pushed into the winding group 6. This is also a shape that is easy to induce soft shorts.

  FIG. 5 is a schematic diagram showing how the battery container contracts in the width direction when the battery container expands in the thickness direction. When the internal pressure of the battery rises abnormally, for example, when the prismatic battery 100 is overcharged, the battery container 5 expands in the thickness direction due to this abnormal increase in internal pressure. Then, the battery container 5 does not change so much even though it is stretched by some plastic deformation. Therefore, the battery container 5 is contracted in the width direction by the amount of expansion in the thickness direction. This contraction appears as a larger deformation at the center in the height direction where there is no holding body other than the battery container 5 than at the end in the height direction of the battery container 5 held by the cover plate (FIG. 5). (See the right figure).

  FIG. 6 is a schematic diagram illustrating a state where the battery container contracts in the width direction and the protrusion is pushed into the wound group. As a result of the central portion of the battery container 5 being greatly contracted, the central portion in the height direction is most deformed and becomes a constricted shape as shown in FIG. Due to this deformation, the protruding portion 8 installed on the inner wall of the battery container 5 is pushed into the wound group 6. At this time, in the central portion in the height direction of the wound group 6 having the largest deformation, the protrusion 8 strongly presses the wound group 6 to cut the separator minutely, and the positive electrode and the negative electrode are brought into contact with each other to make a soft short. To trigger. By this soft short, the electric energy of the battery can be discharged at a low speed.

  By constructing such a mechanism with the protrusions 8, as in the case where there is no such mechanism, most of the separator melts and short-circuits in a large area while the charged state of the electrode is high, and the positive electrode and the negative electrode A large current flows in direct contact with a low resistance, and sudden abnormal heat generation of the battery is caused by the Joule heat of this current, and in some cases, an unsafe behavior of the battery leading to explosion can be prevented.

  As shown in FIG. 4 and FIG. 6, when the protrusion 8 formed on the inner wall of the battery case 5 is divided into two near the center in the height direction and is discontinuous in the height direction, Near the center of the wound group 6 in the height direction, there is an end of the protrusion 8. In this case, since the end of the protrusion 8 cuts the separator minutely, in the soft short induced thereby, the positive electrode and the negative electrode are brought into contact with each other with a higher electric resistance, and the current is smaller. Therefore, it is possible to discharge without generating a large Joule heat.

  In the above embodiment, the protrusion 8 is divided into two in the height direction to make it discontinuous. The protrusion 8 may be divided into three or more in the height direction to be discontinuous, or may not be divided in the height direction (it may not be discontinuous). That is, in the height direction, the number of the protrusions 8 may be one or plural. When the number of the protrusions 8 in the height direction is plural, for example, the number of divisions of the protrusions 8 may be increased and the protrusions 8 may be scattered in the height direction.

  Further, the protruding length of the protrusion 8 may not be uniform. For example, the protruding length of the central portion in the height direction may be larger than the protruding length of other portions. When the protruding portion 8 is divided into two or more in the height direction to be discontinuous, the protruding lengths of the divided protruding portions 8 may be different. Also in this case, for example, the protruding length of the central portion in the height direction can be made larger than the protruding length of the other portions.

  FIG. 7 is a cross-sectional view of the rectangular nonaqueous electrolyte secondary battery taken along line AA ′ in FIG. 3 in the same manner as FIG. 4, and is a diagram in the case where the protrusions 8 are scattered in the height direction. . Thus, when the protrusions 8 are scattered in the height direction, the effect of inducing a soft short by cutting the separator minutely can be further increased.

  Further, when the protrusion 8 is divided into two or more in the height direction, the lengths in the height direction of the divided pieces of the protrusion 8 (one of the divided protrusions 8) may be different from each other. .

  FIG. 8 is a cross-sectional view of the rectangular nonaqueous electrolyte secondary battery taken along line AA ′ in FIG. 3, similar to FIG. 4, and is a view when the protrusion 8 is divided into three in the height direction. is there. The divided piece of the protrusion 8 at the center in the height direction has a shorter length in the height direction than the other divided pieces. Thus, if the length in the height direction of the split piece at the center in the height direction is shortened, the effect of inducing a soft short by finely cutting the separator when the battery container is deformed is further increased. be able to.

  Needless to say, it is effective to appropriately change the number of divisions in the height direction of the protrusions 8 and the length in the height direction of the divided pieces of the protrusions 8 according to the design of the battery.

  In the present embodiment, it has been described that when the protrusion provided on the inner wall of the battery container is discontinuous, it is more likely to become the starting point of the soft short phenomenon. As described above, the protrusions may be continuous or discontinuous in the height direction. Moreover, the optimal cross-sectional shape of the protrusion can be selected regardless of whether it is continuous or discontinuous in the height direction. For example, the cross-sectional shape can be a semicircle with a smaller diameter, or a polygonal shape such as a triangle. In addition, when dividing the protrusions to make them discontinuous in the height direction, a protrusion with a relatively short length in the height direction is provided only at the central part of the battery container having a large deformation, By providing a large protrusion, the separator can be more easily ruptured. Thus, the optimal shape of the protrusion can be selected according to the design of the battery.

  In addition, if the section where the protrusion is present is longer than the section where the wound group exists in the height direction, a soft short occurs not only at the center of the wound group but also at the end of the wound group. It becomes possible. Needless to say, the length of the section where the protrusions exist in the height direction should be determined according to the design of the battery.

  Further, in the battery having a structure in which the curved portion of the winding group is opposed to the cover plate of the battery container, the protrusion may be provided on the inner wall of one or both of the upper cover plate and the bottom cover plate of the battery container. .

  Regardless of which shape is selected, the present invention is effective in inducing a soft short and releasing electric energy at a low speed before reaching an unsafe phenomenon by the protrusion provided on the inner wall of the battery case. It is.

  DESCRIPTION OF SYMBOLS 1 ... Positive electrode terminal, 2 ... Negative electrode terminal, 3 ... Gas discharge valve, 4 ... Injection hole, 5 ... Battery container, 6 ... Winding group, 6a ... Plane part, 6b ... Curved part, 7 ... Current collection component, 8 ... protrusion, 100 ... square battery.

Claims (7)

A square non-aqueous electrolyte secondary battery having a wound group obtained by winding a positive electrode and a negative electrode flatly through a separator, and a battery container storing the wound group,
The wound group has a flat portion and a curved portion forming a flat shape,
The battery container may have a protrusion on the inner wall,
The prismatic non-aqueous electrolyte secondary battery , wherein the protrusion is formed only at a position facing the top of the curved portion of the wound group .   2. The prismatic nonaqueous electrolyte secondary battery according to claim 1, wherein the protrusion is present in a longer section in the winding axis direction of the wound group than a section in which the wound group exists.   The prismatic nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the protrusions are discontinuously present in a winding axis direction of the winding group.   The prismatic nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the battery container has a plurality of the protrusions in a winding axis direction of the winding group.   The prismatic nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the protrusions are scattered in a winding axis direction of the winding group.   The prismatic nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the battery container has the protrusion on an inner wall facing each of the two curved portions of the wound group.   The prismatic non-aqueous electrolyte secondary according to any one of claims 1 to 6, wherein the protrusion has a semicircular shape in which a cross section perpendicular to a winding axis direction of the winding group has a diameter portion having a curvature. battery.

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