JP2015115203A - Battery pack using laminate type battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery pack using a fully packed structure covered with a strong outer case prevented from thermal runaway even in an overcharged state.SOLUTION: Disclosed is a laminate type battery pack which is formed by assembling a plurality of laminate sheets. Since a clearance in a battery pack or between the strong outer case is provided in advance, even if heat is generated by the malfunction such as overcharge and external heating, ignition due to thermal runaway can be prevented by providing expansion buffer of a cell and promoting heat release by increasing a surface area even if the cell is expanded.

Description

The present invention relates to an assembled battery using a plurality of laminated batteries, and more particularly, to an assembled battery structure that does not run out of heat even in an overcharged state without providing a special cooling mechanism.

  In recent years, with the development of portable electronic devices such as mobile phones and notebook computers, and the practical application of electric vehicles, the demand for electrochemical elements such as high-energy density non-aqueous secondary batteries has increased rapidly. Currently, non-aqueous secondary batteries that can meet these requirements include, for example, a positive electrode using a lithium composite oxide that can be doped and dedoped with lithium ions, a material that can be doped and dedoped with lithium ions, and lithium metal. Lithium secondary batteries constructed by enclosing the negative electrode used and a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in an organic solvent in a laminate or a metal exterior material are widely used, especially battery cars In a large battery for power storage, a plurality of lithium secondary batteries are used as an assembled battery.

  In an assembled battery using a plurality of lithium secondary batteries, a plurality of laminated batteries are often used by covering them with an outer case. For example, as described in Patent Document 1, first, the stacked battery group is covered with a simple exterior case (core pack), and an electric substrate such as a protection circuit is connected to the battery group as necessary. In some cases, a final assembled battery may be obtained by covering with a strong outer case (full pack).

JP 2009-259581 A JP2013-168387A

Lithium secondary batteries use flammable organic solvents as non-aqueous electrolytes, so safety measures are important. For this reason, safety is confirmed using test conditions under excessive use conditions. For example, in an overcharge test, it is checked whether a dangerous state such as ignition will occur even if the battery is fully charged, assuming that the protection circuit has failed. When the overcharge test is performed, the safety of the battery pack varies greatly depending on the state of incorporation in the outer case, and it does not ignite in a simple outer case such as a core pack, but in a strong outer case such as a full pack. There is an event that ends up. In the case of the core pack, when the temperature rises due to overcharging, the outer case is destroyed due to cell expansion, and the cells bundled in the pack are scattered in an accordion shape. In the case of a full pack, the outer case is strong so that the shape is maintained without being destroyed. By releasing the core pack, the contact area with the air is increased and the heat is dissipated, so that the thermal runaway does not lead to ignition, but the full pack does not dissipate heat, so it is considered that the thermal runaway occurs.

  The present invention uses this phenomenon to prevent ignition by providing a space that can be expanded conversely as a buffer.

  In order to achieve the above object, the present invention is characterized in that, in an assembled battery using a plurality of laminated batteries, a gap is provided in advance in the assembled battery or between the outer case and the assembled battery. Even if the battery abnormally heats up due to a malfunction such as overcharge or external heating, by providing a gap that becomes an expansion buffer, the gap between the laminated batteries expanded due to abnormal heat generation increases the heat dissipation and thermal runaway It is possible to prevent ignition due to. Among the assembled batteries using a plurality of laminated batteries, by expanding the interval only around some of the single cells constituting the assembled battery, it is possible to promote heat dissipation and prevent ignition due to thermal runaway.

  In addition, among battery packs using multiple laminated batteries, the distance between only the single-sided or double-sided battery cells located at the outermost end of the battery pack is widened to promote heat dissipation and prevent thermal runaway. I can do it. By setting the part that provides the expansion buffer gap to the position of the unit cell that is the outermost end, other unit batteries are configured integrally, so that the rigidity of the assembled battery unit is not lost as much as possible It becomes possible to.

  In addition, among battery packs using a plurality of laminated batteries, widening the gap only around the single or multiple battery cells located at the center of the battery pack promotes heat dissipation and prevents thermal runaway. I can do it. The central part of the battery pack that stores the most heat and is most difficult to dissipate is the central part of the battery pack, so that the high-temperature part of the battery pack is concentrated. It is possible to dissipate heat and prevent thermal runaway.

  Furthermore, when one or a plurality of low-capacity laminated batteries exist in a part of a battery pack using a plurality of laminated batteries, the interval is limited only to the periphery of the single battery or a plurality of single-cell batteries having a low capacity. By expanding, heat dissipation can be promoted and thermal runaway can be prevented. Normally, it is the single battery with the least capacity that is likely to be overcharged in the assembled battery, so a low-capacity battery that is likely to be overcharged is incorporated in the assembled battery, and a gap serving as an expansion buffer is provided in that part to reduce the battery capacity. Avoiding overcharging of other batteries than the capacity, and the heat dissipation efficiency around the low-capacity battery is high, so that thermal runaway due to overcharging can be prevented.

  According to the present invention, by providing a space that can be expanded in a part of a battery pack pack as a buffer in advance, heat can be efficiently dissipated when the battery expands due to overcharge or the like, thereby preventing thermal runaway of the battery. It becomes possible.

It is a schematic diagram of a laminate type battery. It is the schematic diagram which made the some laminated type battery by this invention into the pack, and was set as the assembled battery. It is a schematic diagram when a battery expand | swells. It is a schematic diagram which shows embodiment which provided the clearance gap in the center part. It is a mimetic diagram showing an embodiment incorporating a low capacity battery.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The lithium secondary battery used in the present invention is a laminate type battery having an aluminum laminate on a positive electrode, a negative electrode, a separator, a nonaqueous electrolyte, and an exterior. FIG. 1 shows a schematic diagram of a laminated battery. The positive electrode 2 is obtained by mixing a positive electrode active material, a conductive additive and a binder in an organic solvent, and coating, drying and rolling the composition on an aluminum foil to form a positive electrode layer. The negative electrode 3 was prepared by mixing a negative electrode active material mainly composed of a carbon material, a binder and, if necessary, a conductive additive, applying the composition onto a copper foil, drying and rolling in the same manner as the positive electrode 2. Is a negative electrode layer. A separator made of a polymer is disposed between the positive electrode layer and the negative electrode layer.

  An electrode body composed of a positive electrode, a negative electrode, and a separator has a laminated electrode body structure in which, for example, a positive electrode and a negative electrode cut out to a predetermined size are stacked while folding a strip-shaped separator. The positive electrode lead 4 from the positive electrode 2 and the negative electrode lead 5 from the negative electrode 3 are drawn out of the outer aluminum laminate 1. An opening is made without sealing only one side of the cell for liquid injection, and the other parts are thermally welded to prepare a battery before liquid injection. Next, a nonaqueous electrolytic solution is injected, one side where the injection portion is open is sealed by thermal fusion, and then the initial charge is performed. An initial gas generation occurs due to the initial charging, and an aging process in which the cell is allowed to stand for several hours in an environment of 20 to 80 ° C., after the generated gas is removed, and heat fusion is performed while drawing a vacuum, and then scheduled. The battery is fully charged to the current battery voltage, and a lithium secondary battery is created.

  There is no restriction | limiting in particular about the other structure and structure of a lithium secondary battery, The structure and structure conventionally known can be applied.

  FIG. 2 is a schematic view showing a battery pack in which a plurality of laminated batteries are packed. A plurality of unit cells 8 of a laminate type battery are accommodated in the outer case 6, and a gap with the outer case is provided on both the upper side and the lower side of the unit cell assembly, and the battery is abnormal. When it expands due to heat generation or the like, it functions as an expansion buffer 8.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

(Example 1)
<Preparation of positive electrode>
94 parts by mass of a positive electrode active material represented by LiCoO ₂ , 4 parts by mass (as solid content) of PVDF (10% NMP solution) as a binder, 1 part by mass of artificial graphite as a conductive assistant, and Ketjen 1 part by mass of black was kneaded using a planetary mixer, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing composition.

  After applying the positive electrode mixture-containing composition to both surfaces of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, vacuum drying is performed at 120 ° C. for 12 hours to form a positive electrode mixture layer on both surfaces of the aluminum foil. Formed. Then, the press process was performed and the thickness and density of the positive mix layer were adjusted. The resulting positive electrode was cut out to a predetermined size using a Thomson blade to obtain a positive electrode.

<Production of negative electrode>
Water was added to 97.5 parts by mass of natural graphite having an average particle diameter of 10 μm as a negative electrode active material, 1.5 parts by mass of styrene butadiene rubber as a binder, and 1 part by mass of carboxymethyl cellulose as a thickener. In addition, the mixture was mixed to prepare a negative electrode mixture-containing paste. This negative electrode mixture-containing paste was applied to both sides of a copper foil having a thickness of 8 μm, and then vacuum-dried at 120 ° C. for 12 hours to form negative electrode mixture layers on both sides of the copper foil. Then, the press process was performed and the thickness and density of the negative mix layer were adjusted. The produced negative electrode was cut out to a predetermined size using a Thomson blade to obtain a negative electrode.

<Preparation of electrolyte>
LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a volume ratio of 2: 3: 1, 2.5% by mass of vinylene carbonate was added, and the electrolytic solution was Prepared.

<Battery assembly>
The positive electrode and the negative electrode were alternately stacked while the heat-resistant separator (porosity: 43%) in which inorganic particles were applied on one side of the cut positive electrode and the negative electrode with a thickness of 16 μm were folded to produce an electrode laminate. . The separator was composed of a 12 μm polyethylene layer and a 4 μm boehmite layer, and was laminated so that the boehmite layer faced the positive electrode side to prepare a laminate of 7 positive electrodes and 8 negative electrodes. At this time, the protruding length from the negative electrode in the separator width direction was set to 0.75 mm. The end of the separator in the longitudinal direction was fixed with an insulating tape made of polypropylene. An aluminum lead was welded to the exposed portion of the aluminum foil of the positive electrode. A propylene-based resin film for improving the heat-welding property was attached to the lead. For the negative electrode, a lead made of nickel was welded to the exposed portion of the copper foil in the same manner as the positive electrode. A propylene-based resin film for improving the heat-welding property was attached to the lead. Thereafter, both end portions in the width direction of the separator of the laminate are thermally welded using a heat sealer, and a depression having a size that can accommodate the laminate in advance is prepared on an outer laminate sheet of 114 μm, and the electrode laminate is provided therein. Stowed. After housing the electrode laminate, the opening was thermally welded with a heat sealer. The resulting pre-injection battery was vacuum dried at 60 ° C. for 12 hours. Thereafter, a non-aqueous electrolyte was injected from the three portions opened on one side, and the three portions were immediately sealed by heat welding. The dimensions of the produced laminated lithium secondary battery are 161 mm in length, 78 mm in width, and 6.5 mm in thickness.

  Next, eight of these laminate type secondary batteries were connected in series and stored in an outer case. Batteries 1 to 8 were bound to the outer case, and a space was formed between the upper and lower sides of the bound battery and the outer case to prepare an assembled battery.

(Example 2)
Among the eight laminated secondary batteries housed in the outer case, the assembled battery is the same as in Example 1 except that a space is provided around the two laminated batteries arranged in the center as shown in FIG. It was created.

(Example 3)
Of the eight laminated secondary batteries stored in the outer case, in order to confirm the effect of the present invention, as shown in FIG. An assembled battery was produced in the same manner as in Example 1 except that the space was further changed and a space was provided around the periphery.

(Comparative Example 1)
An assembled battery was prepared in the same manner as in Example 1 except that the space between the upper and lower sides of the bound battery and the outer case was not provided.

<Overcharge test>
As a condition for overcharging, when constant current charging was performed up to 120% of the upper limit charging voltage at the maximum charging current, some cells expanded due to heat generation, and the assembled battery of Example 1 was in the state shown in FIG. However, there was no ignition. Similarly, in the assembled batteries of Examples 2 and 3, thermal runaway did not occur and ignition did not occur. On the other hand, since the battery of Comparative Example 1 was not provided with an expansion buffer in the outer case, the outer case was damaged by expansion of some or all of the cells.

DESCRIPTION OF SYMBOLS 1 Laminate exterior material 2 Positive electrode 3 Negative electrode 4 Positive electrode lead 5 Negative electrode lead 6 Exterior case 7 Expansion buffer 8 Unit cell 9 Expanded cell 10 Low capacity cell

Claims (5)

In an assembled battery using a plurality of laminate-type batteries, the assembled battery is housed in an outer case, and when the laminated battery expands in the outer case, a gap is provided for accommodating an expansion portion. Assembled battery. 2. The assembled battery according to claim 1, wherein the interval is widened only around a part of the single cells constituting the assembled battery. The assembled battery according to claim 2, wherein a space only around the single-sided or double-sided cell located at the outermost end constituting the assembled battery is widened. The assembled battery according to claim 2, wherein only the periphery of the single or a plurality of single cells located at the center of the assembled battery is widened. 5. The assembled battery according to claim 4, wherein among the single cells constituting the assembled battery, the interval only around the low-capacity single cells is expanded compared to other single cells.

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