JP2015130292A - power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent short circuit and make shut down less liable to occur even when a separator early in shut down exceeds a contracting temperature in a case where two types of separator, one is a separator early in shut down and the other is a separator less liable to contract or not contract, is used.SOLUTION: A secondary battery has an electrode assembly 12 in which a positive pole 14 and a negative pole 15 are arranged in layers with a separator 16 between them. The separator 16 is configured such that a heat resistant layer 16c smaller in coefficient of friction than the first separator 16a is present between the first separator 16a and second separator 16b. The first separator 16a is arranged on the positive pole 14 side and the second separator 16b is arranged on the negative pole 15 side. The first separator 16a is higher in contraction start temperature than the second separator 16b. The heat resistant layer 16c is higher in heat resistance than the first separator 16a. The second separator 16b is configured independently of the first separator 16a and heat resistant layer 16c.

Description

  The present invention relates to a power storage device, and more particularly to a power storage device characterized by a separator interposed between a positive electrode and a negative electrode.

  The separator plays a role of forming an ion conduction path between the electrodes (between the positive electrode active material layer and the negative electrode active material layer) by preventing the short circuit due to the contact between the positive electrode and the negative electrode and holding the electrolytic solution. Yes. In addition to the short-circuit prevention function, lithium ion secondary battery separators block the ion conduction path when the battery reaches a certain temperature range (typically the melting point (or softening point) of the separator). Therefore, a function (shutdown function) that stops charging and discharging and prevents thermal runaway of the battery is required.

  As a separator for a lithium ion secondary battery, a separator shown in FIG. 7 has been proposed. The separator 50 has a configuration in which a ceramic layer 70 is provided on the first surface of the substrate 60. The base material 60 has a mode in which a porous PE (polyethylene) layer 61 as an inner layer is sandwiched between porous PP (polypropylene) layers 62 and 63 as outer layers. The porous PP layer 62 has a surface modification layer 62 a at the interface with the ceramic layer 70. The ceramic layer 70 includes at least an inorganic filler and a binder.

JP 2011-71009 A

  During use of the lithium ion secondary battery, the negative electrode generates a large amount of heat, for example, from 100 to 180 ° C., and the positive electrode generates a large amount of heat, for example, at 180 ° C. or higher. When the separator is a single PP layer, the shutdown is slow and the shrinkage is small. When the separator is a single PE layer, the shutdown is quick and the shrinkage is large. In the PP / PE / PP3 layer, the shutdown is fast and the contraction is moderate. However, in the case where the PP / PE / PP3 layers are heat-welded and integrated, PP is also pulled and contracted by the stress when PE contracts.

  In the separator 50 of Patent Document 1, since the ceramic layer 70 is applied to one porous PP layer 62, the shrinkage is smaller than that of a simple PP / PE / PP three-layer structure, but the negative electrode generates heat in the porous PE layer. There is a problem that it is difficult to be transmitted to the layer 61 and it is difficult to shut down.

  The present invention has been made in view of the above problems, and its object is to use a separator that shuts down quickly when it uses two types of separators: a separator that shuts down quickly and a separator that does not shrink easily or does not shrink. It is an object of the present invention to provide a power storage device that can prevent a short circuit and does not easily shut down even when the temperature at which it shrinks.

  A power storage device that solves the above problem is a power storage device having an electrode assembly in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween. The separator has a configuration in which a heat-resistant layer having a smaller friction coefficient than the first separator exists between the first separator and the second separator, the first separator is disposed on the positive electrode side, and the second separator A separator is disposed on the negative electrode side, the first separator has a higher shrinkage start temperature than the second separator, the heat resistant layer has a higher heat resistance than the first separator, and the second separator has the first separator. And it is comprised separately from the said heat-resistant layer. Here, “small friction coefficient” means that welding of the second separator that has reached the melting temperature can be prevented. In addition, “the shrinkage start temperature is high” includes a case where the shrinkage does not shrink.

  According to this configuration, for example, when the positive electrode and the negative electrode are abnormally heated due to overcharging in the usage state of the power storage device, the second separator melts before the first separator reaches the contraction temperature due to the heat from the negative electrode. The fine pores of the separator are blocked by melting or softening, and the charging is stopped by blocking the ion conduction between the electrodes. That is, the shutdown is performed. Thereafter, the second separator contracts as the temperature rises. When there is no heat-resistant layer having a smaller friction coefficient than the first separator between the first separator and the second separator, the second separator shrinks in a state where it is welded to the first separator. Power is added. As a result, the first separator is contracted by the contraction force of the second separator before reaching the contraction temperature.

  However, since a heat-resistant layer having a smaller friction coefficient than that of the first separator exists between the first separator and the second separator, welding of the second separator to the first separator is prevented, and the first separator has its contraction temperature. It is prevented from being contracted by the contraction force of the second separator before reaching. Therefore, when two types of separators are used, a separator that shuts down quickly and a separator that does not shrink easily or does not shrink, even if the temperature of the separator that shuts down quickly exceeds the temperature at which the separator shrinks, a short circuit can be prevented and shutdown can be prevented. There is no difficulty.

  The heat-resistant layer is preferably formed integrally with the first separator. The heat-resistant layer may be provided independently of the first separator. However, when the heat-resistant layer is formed integrally with the first separator, the heat-resistant layer is provided between the first separator and the second separator in the assembly process of the electrode assembly. The work of sandwiching is no longer necessary, and the work in the assembly process is simplified.

  Preferably, the second separator is formed in a bag shape, and the heat-resistant layer, the first separator, the positive electrode, the first separator, and the heat-resistant layer stacked in this order are accommodated in the second separator. . According to this configuration, in the assembly process of the electrode assembly, the positive electrode, the negative electrode, the first separator, the second separator, and the heat-resistant layer are laminated in a predetermined arrangement order by alternately arranging the negative electrode and the second separator. Can be made easier.

  According to the present invention, when two types of separators, that is, a separator that shuts down quickly and a separator that does not shrink easily or does not shrink, a short circuit can be prevented even if the temperature at which the separator that shuts down quickly shrinks is exceeded. It can be done and it is not difficult to shut down.

The schematic cross section of the secondary battery of 1st Embodiment. The model perspective view of an electrode assembly. The schematic cross section which shows the positional relationship of a positive electrode, a separator, and a negative electrode. The schematic cross section explaining an operation. (A), (b) is a schematic cross section explaining the effect | action of a comparative example. The schematic cross section which shows the positional relationship of the positive electrode of 2nd Embodiment, a separator, and a negative electrode. The schematic cross section of the separator of a prior art.

(First embodiment)
A first embodiment in which the present invention is embodied in a lithium ion secondary battery will be described below with reference to FIGS.

  As shown in FIG. 1, in a secondary battery 10 as a power storage device, a laminated electrode assembly 12 is accommodated together with an electrolyte solution 13 in a rectangular parallelepiped case 11. The case 11 includes a bottomed rectangular cylindrical metal case body 11a and a lid 11b that closes the opening of the case body 11a.

  As shown in FIG. 2, the electrode assembly 12 includes a positive electrode 14 having an active material layer 14b on a metal foil 14a and a negative electrode 15 having an active material layer 15b on the metal foil 15a, with a separator 16 interposed therebetween. In this state, a plurality of layers are stacked. The active material layers 14b and 15b are formed on both surfaces of the metal foils 14a and 15a constituting the positive electrode 14 and the negative electrode 15, respectively.

  The positive electrode 14 includes a metal foil 14a formed in a substantially rectangular shape, an active material layer 14b formed by applying and drying an active material mixture on both surfaces thereof, and a positive electrode tab extending from one side of the metal foil 14a. 14c. Further, the positive electrode 14 has an active material non-applied portion 14d where the active material layer 14b is not formed along the side of the metal foil 14a where the positive electrode tab 14c is formed.

  The negative electrode 15 includes a metal foil 15a formed in a substantially rectangular shape, an active material layer 15b formed by applying and drying an active material mixture on both sides thereof, and a negative electrode tab extending from one side of the metal foil 15a. 15c. The metal foil 15 a of the negative electrode 15 and the metal foil 14 a of the positive electrode 14 are formed in the same size, and the area of the active material layer 15 b of the negative electrode 15 is larger than the area of the active material layer 14 b of the positive electrode 14. Therefore, unlike the positive electrode 14, the negative electrode 15 does not have an active material non-coated portion where the active material layer 15 b is not formed along the side of the metal foil 15 a where the negative electrode tab 15 c is formed. Note that the thickness of the active material layers 14b and 15b is equal to or greater than the thickness of the metal foils 14a and 15a. However, in the cross-sectional views of FIG. 15, the thickness of the active material layers 14b and 15b is ignored.

  In the electrode assembly 12, the laminated body of the positive electrode tabs 14 c is electrically connected to the positive electrode terminal 18 through the positive electrode conductive member 17, and the laminated body of the negative electrode tab 15 c is connected through the negative electrode conductive member 19. It is electrically connected to the negative terminal 20. The positive terminal 18 and the negative terminal 20 are electrically insulated from the case 11.

  As shown in FIGS. 2 and 3, the separator 16 has a configuration in which a heat-resistant layer 16c having a smaller friction coefficient than the first separator 16a exists between the first separator 16a and the second separator 16b, and the first separator 16a. Is disposed on the positive electrode 14 side, and the second separator 16b is disposed on the negative electrode 15 side. The heat-resistant layer 16c is formed integrally with the first separator 16a. For example, the heat-resistant layer 16c is formed in a state where it is applied to the first separator 16a. The second separator 16b is configured separately from the first separator 16a and the heat-resistant layer 16c.

  The first separator 16a has a shrinkage start temperature higher than that of the second separator 16b, and the heat-resistant layer 16c has heat resistance higher than that of the first separator 16a. The first separator 16a is made of porous PP (polypropylene), and the second separator 16b is made of porous PE (polyethylene). The heat-resistant layer 16c is formed as a porous coat layer containing ceramic particles (powder).

Next, the operation of the secondary battery 10 configured as described above will be described.
The secondary battery 10 is modularized in a state where the plurality of secondary batteries 10 are pressurized so that the side walls of the case 11 are flat. Therefore, in the use state of the secondary battery 10, as shown in FIG. The load is applied.

  The PE constituting the second separator 16b has a shutdown temperature of, for example, about 130 ° C. and a shrinkage temperature (shrinkage start temperature) of, for example, about 145 to 160 ° C. On the other hand, the PP constituting the first separator 16a has a shutdown temperature of, for example, about 170 ° C. and a shrinkage temperature of, for example, about 180-200 ° C. The shutdown occurs when the pores are blocked when the temperature of the porous PE or the porous PP becomes higher than the melting point or the softening point. Further, the negative electrode 15 generates a large amount of heat, for example, from 100 to 180 ° C., and the positive electrode 14 generates a large amount of heat, for example, at 180 ° C. or higher.

  When the secondary battery 10 is in use, for example, when the positive electrode 14 and the negative electrode 15 abnormally generate heat due to overcharge or overdischarge, the secondary battery 10 is shut down before reaching the contraction temperature of the first separator 16a that is difficult to contract. Thus, it is possible to avoid occurrence of a short circuit. Since the second separator 16b is in contact with the negative electrode 15, the heat of the negative electrode 15 is efficiently transmitted to the second separator 16b. Then, due to the heat generated by the negative electrode 15, the second separator 16b melts and shuts down before the first separator 16a reaches the contraction temperature.

  When the second separator 16b melts and contracts, a force F acts on the adjacent heat-resistant layer 16c in the direction indicated by the arrow in FIG. 4, but the heat-resistant layer 16c has a small coefficient of friction, so that the heat-resistant layer 16c has a small friction coefficient. The welding of the second separator 16b is prevented, and the first separator 16a is prevented from being contracted by the contracting force of the second separator 16b before reaching the contraction temperature.

  As shown in FIG. 5A, when the second separator 16b, the heat-resistant layer 16c, and the first separator 16a are arranged in this order from the positive electrode 14 side between the positive electrode 14 and the negative electrode 15, the heat generation of the negative electrode 15 is the first. It is difficult to transmit to the second separator 16b, and the second separator 16b is difficult to shut down. As a result, the current continues to flow, the temperature rises and there is a risk of a short circuit.

  Further, as shown in FIG. 5B, when a separator in which the heat-resistant layer 16c is integrally formed with the second separator 16b without using the first separator 16a is used, the shrinkage start temperature of the second separator 16b is The temperature rises by about 5 ° C. compared to the configuration without the heat-resistant layer 16c. However, since the first separator 16a does not exist, if the shrinkage start temperature increases by about 5 ° C., the heat resistant layer 16c may be shrunk integrally due to the shrinkage of the second separator 16b after the start of shrinkage of the second separator 16b, thereby causing a short circuit. There is.

According to this embodiment, the following effects can be obtained.
(1) The secondary battery 10 is a power storage device having an electrode assembly 12 in which a positive electrode 14 and a negative electrode 15 are stacked with a separator 16 interposed therebetween. The separator 16 has a configuration in which a heat-resistant layer 16c having a smaller friction coefficient than the first separator 16a exists between the first separator 16a and the second separator 16b, and the first separator 16a is disposed on the positive electrode 14 side, The separator 16b is disposed on the negative electrode 15 side. The first separator 16a has a higher shrinkage start temperature than the second separator 16b, the heat resistant layer 16c has a higher heat resistance than the first separator 16a, and the second separator 16b is configured separately from the first separator 16a and the heat resistant layer 16c. Has been. Therefore, when two types of separators, ie, a separator that shuts down quickly (second separator 16b) and a separator that does not easily shrink (first separator 16a) are used, a short circuit occurs even if the temperature at which the separator that shuts down quickly exceeds the shrinking temperature. Can be prevented, and it is not difficult to shut down.

  (2) The heat-resistant layer 16c is formed integrally with the first separator 16a. The heat-resistant layer 16c may be provided independently of the first separator 16a. However, when the heat-resistant layer 16c is formed integrally with the first separator 16a, the first separator 16a and the second separator 16b are assembled in the assembly process of the electrode assembly 12. The work of sandwiching the heat-resistant layer 16c between them is not necessary, and the work in the assembly process is simplified.

(Second Embodiment)
Next, a second embodiment will be described with reference to FIG. This embodiment is different from the first embodiment in that the second separator 16b is formed in a bag shape, and the positive electrode 14, the first separator 16a, and the heat-resistant layer 16c are accommodated in the bag-shaped second separator 16b. ing. The same parts as those in the first embodiment are denoted by the same reference numerals and detailed description thereof is omitted.

  As shown in FIG. 6, in the bag-shaped second separator 16b, the positive electrode 14 is disposed in the center in the stacking direction, and the first separator 16a and the heat-resistant layer 16c are provided on both sides of the positive electrode 14, respectively. The positive electrode 14 and the heat-resistant layer 16c are accommodated in a state facing the second separator 16b.

  In the assembly process of the electrode assembly 12, after a predetermined number of negative electrodes 15 and second separators 16b are alternately arranged, the laminate of the positive electrode tabs 14c is welded to the conductive member 17 for the positive electrode, and the laminate of the negative electrode tabs 15c. Are welded to the conductive member 19 for the negative electrode to form the electrode assembly 12.

  Also in this embodiment, the first separator 16a, the second separator 16b, and the heat-resistant layer 16c exist between the adjacent positive electrode 14 and negative electrode 15 constituting the electrode assembly 12. The heat-resistant layer 16c is disposed between the first separator 16a and the second separator 16b, the first separator 16a is disposed on the positive electrode 14 side, and the second separator 16b is disposed on the negative electrode 15 side.

Therefore, according to the second embodiment, the following effects can be obtained in addition to the same effects as (1) and (2) of the first embodiment.
(3) The second separator 16b is formed in a bag shape, and a layer in which the heat-resistant layer 16c, the first separator 16a, the positive electrode 14, the first separator 16a, and the heat-resistant layer 16c are stacked in this order is accommodated in the bag-shaped second separator 16b. Has been. According to this configuration, in the assembly process of the electrode assembly 12, the negative electrode 15 and the second separator 16b are alternately arranged, whereby the positive electrode 14, the negative electrode 15, the first separator 16a, the second separator 16b, and the heat-resistant layer 16c. Can be stacked in a predetermined arrangement order, and the operation becomes easier.

The embodiment is not limited to the above, and may be embodied as follows, for example.
The first separator 16a is not limited to porous PP, but may have any electrical insulation, a contraction start temperature higher than that of the second separator 16b, and any structure that can retain an electrolyte and secure an ion conduction path. For example, it may be paper or non-woven fabric. The nonwoven fabric is made of resin fibers selected from, for example, polypropylene, polyamide, and polyethylene terephthalate. Paper is also considered a cellulose nonwoven fabric. Further, although the paper does not shrink even when the temperature becomes high, the shrinkage start temperature is substantially higher than that of the second separator 16b. That is, the fact that the shrinkage start temperature is higher than that of the second separator 16b includes not shrinking even when the temperature becomes high.

The heat-resistant layer 16c is not limited to the structure formed integrally with the first separator 16a, and may be a structure formed separately from the first separator 16a.
The positive electrode 14 and the negative electrode 15 are not limited to the configuration in which the active material layers 14b and 15b are formed on both surfaces of the metal foils 14a and 15a, and the active material layers 14b and 15b are formed only on one surface of the metal foils 14a and 15a. It may be a configuration.

  ○ Even when using the positive electrode 14 and the negative electrode 15 in which the active material layers 14b and 15b are formed on both surfaces of the metal foils 14a and 15a, the metal foils 14a and 15a You may use the positive electrode 14 and the negative electrode 15 in which the active material layers 14b and 15b were formed in the single side | surface. In this case, since the unnecessary active material layers 14b and 15b are not present, the active material is not wasted.

  ○ The positive electrode tab 14c and the negative electrode tab 15c are not limited to those integrally formed by using a part of the metal foils 14a and 15a, and a separately formed metal foil for tabs is joined to the active material non-coated portion by welding. It is good also as a structure.

The electrode assembly 12 is not limited to the laminated type, and may be a wound type electrode assembly 12.
The secondary battery 10 is not limited to a lithium ion secondary battery, and may be another secondary battery such as a nickel hydrogen secondary battery or a nickel cadmium secondary battery.

The power storage device is not limited to the secondary battery 10 and may be a capacitor such as an electric double layer capacitor or a lithium ion capacitor.
The following technical idea (invention) can be understood from the embodiment.

  (1) The power storage device according to claim 1 or 2, wherein the second separator is formed in a bag shape, and the negative electrode is accommodated in the second separator.

  DESCRIPTION OF SYMBOLS 10 ... Secondary battery as an electrical storage device, 12 ... Electrode assembly, 14 ... Positive electrode, 15 ... Negative electrode, 16 ... Separator, 16a ... 1st separator, 16b ... 2nd separator, 16c ... Heat-resistant layer.

Claims (3)

A power storage device having an electrode assembly in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween,
The separator has a configuration in which a heat-resistant layer having a smaller friction coefficient than the first separator exists between the first separator and the second separator, the first separator is disposed on the positive electrode side, and the second separator is Arranged on the negative electrode side, the first separator has a higher shrinkage start temperature than the second separator, the heat resistant layer has a higher heat resistance than the first separator, the second separator includes the first separator and the A power storage device comprising a heat resistant layer and a separate body.   The power storage device according to claim 1, wherein the heat-resistant layer is formed integrally with the first separator.   The said 2nd separator is formed in a bag shape, and what laminated | stacked in order of the said heat resistant layer, the said 1st separator, the said positive electrode, the said 1st separator, and the said heat resistant layer is accommodated in the said 2nd separator. The power storage device described in 1.