JP2013114863A - Stacked secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated secondary battery having high safety when abnormal temperature rises.
SOLUTION: A so-called bipolar type or monopolar having an electrode body in which a plurality of electrode plates are stacked in a single cell layer while sandwiching a separator between a positive electrode active material layer and a negative electrode active material layer. Type laminated secondary battery is an object of the present invention. The multilayer secondary battery according to the present invention further includes a single cell layer positioned in the center of the stacking direction, and includes a single cell layer other than the single cell layers other than the single cell layers near the center. It is characterized by being lower than the shutdown temperature.
[Selection] Figure 1

Description

  The present invention relates to a stacked secondary battery having an electrode body in which a plurality of metal foils having a positive electrode active material layer or a negative electrode active material layer formed on a surface thereof are stacked in a stacked manner with a separator interposed therebetween.

  Secondary batteries are used in a wide variety of fields because they can obtain repeated discharge power by charging. For example, power sources for electronic devices such as mobile phones and notebook computers, and power sources for vehicles such as hybrid cars and electric cars. These secondary batteries generally have an electrode body in which a plurality of metal foils having a positive electrode active material layer or a negative electrode active material layer formed on the surface thereof are overlapped with a separator interposed therebetween. .

  By the way, it is important for secondary batteries to ensure safety when the temperature rises. This is because a so-called thermal runaway state may occur. Patent document 1 is mentioned as a prior art which ensures this safety | security. Patent Document 1 discloses a technique using both a positive electrode active material layer and a separator having high heat resistance. Furthermore, it is considered that it is preferable to dispose a positive electrode active material layer and a separator having higher heat resistance near the center of the secondary battery where the temperature is likely to rise. As a result, the secondary battery can be made highly durable when its temperature rises.

JP 2007-335294 A

  By the way, in a secondary battery, for example, due to a malfunction of the control system, overcharge that is charged beyond its full charge capacity may occur. Usually, overcharging is prevented by a so-called separator shutdown function that physically stops the overcharge. That is, the separator which is a porous film is softened at a temperature near its softening point due to a temperature rise accompanying overcharge. At this time, the separator that is softened and whose pores are closed excessively increases the resistance between the positive and negative electrodes. Thereby, even in a state where the control system is out of order, the charge / discharge reaction of the secondary battery can be physically stopped.

  However, the softening point of the high heat-resistant separator used in the above-described prior art is high. A separator with a high softening point is used in the vicinity of the center of the secondary battery where the temperature is most likely to rise during overcharging. For this reason, there is a problem that the shutdown does not occur easily and the overcharge of the secondary battery cannot be suitably prevented.

  The present invention has been made for the purpose of solving the problems of the prior art described above. That is, the problem is to provide a stacked secondary battery that is highly safe at the time of abnormal temperature rise.

  In order to solve this problem, the laminated secondary battery of the present invention comprises two current collector plates each having a positive electrode active material layer or a negative electrode active material layer formed on at least one surface of a current collector foil, and a current collector foil. Two or more intermediate electrode plates each having a positive electrode active material layer or a negative electrode active material layer formed on both sides, and a separator, two end electrode plates are positioned at both ends of the stack, and between the two end electrode plates Two or more intermediate electrode plates are positioned on each other, a separator is always sandwiched between the electrode plates, and the positive electrode active material layer and the negative electrode active material layer face each other with each separator interposed therebetween. A stacked secondary battery having electrode bodies that are stacked in a stacked manner, including a single battery layer positioned in the center of the stacking direction and including a single battery layer at the center and not including a single battery layer at both ends. The shutdown temperature at which discharge stops is It is stacked secondary battery, characterized lower than the shutdown temperature of the single cell layer other than that.

  One aspect of the electrode body of the laminated secondary battery is a positive end electrode plate in which a positive electrode active material layer is formed on one side of a current collector foil, and a negative end in which a negative electrode active material layer is formed on one side of the current collector foil. An electrode plate, two or more intermediate electrode plates having a positive electrode active material layer formed on one surface of the current collector foil and a negative electrode active material layer formed on the other surface, a separator, and a positive electrode plate and a negative electrode plate Located at both ends of the stack, two or more intermediate electrode plates are located between the positive electrode plate and the negative electrode plate, a separator is always sandwiched between the electrode plates, and the positive electrode active material sandwiching each separator This is an electrode body in which a layer and a negative electrode active material layer face each other so as to form a single battery layer.

  Another aspect of the electrode body of the above-described laminated secondary battery is that two electrode plates each having a positive electrode active material layer or a negative electrode active material layer formed on at least one surface of the current collector foil, and a current collector foil One or more intermediate positive electrode plates having a positive electrode active material layer formed on both sides, one or more intermediate negative electrode plates having a negative electrode active material layer formed on both sides of the current collector foil, a separator, The two end electrode plates are positioned at both ends of the stack, the intermediate positive electrode plate and the intermediate negative electrode plate are positioned between the two end electrode plates, and a separator is always sandwiched between the electrode plates, and In this electrode body, the positive electrode active material layer and the negative electrode active material layer face each other with each separator interposed therebetween, and are stacked in a single cell layer.

  When overcharge occurs in the stacked secondary battery having the electrode body as described above, the temperature of the single battery layer located at the center in the stacking direction is likely to rise. For this reason, the stacked secondary battery of the present invention has a configuration in which shutdown occurs at the lowest temperature in the single cell layer located at least in the center in the stacking direction. As a result, when overcharge occurs, it can be suitably stopped to avoid a thermal runaway state.

  In the above-described stacked secondary battery, the separator included in the center-side single cell layer group preferably has a lower softening point than the separators included in the other single cell layers. This is because the stacked secondary battery can be configured such that shutdown occurs at the lowest temperature in the single battery layer positioned at least in the center in the stacking direction.

  Further, in the above-described stacked type secondary battery, the separator included in the single cell layer group near the both ends including the single cell layer positioned at both ends in the stacking direction and not including the central single cell layer, The softening point is preferably higher than that of the separator included in the single battery layer.

  Depending on the usage environment of the secondary battery, the external temperature may rise excessively. In this case, among the single cell layers, the temperature of the single cell layers located at both ends in the stacking direction is most likely to rise. This is because it is closest to the outside of the secondary battery and is susceptible to the temperature. For this reason, the battery cell separators located at both ends in the stacking direction need to have heat resistance. This is because, when the separator is completely melted and a hole is formed, the positive electrode active material layer and the negative electrode active material layer in that part may come into contact with each other to cause a short circuit. Therefore, when the external temperature rises excessively, it is preferable that the softening points of the separators of the single cell layers located at both ends in the stacking direction are high. As a result, the heat resistance against external heating of the secondary battery can be increased.

  According to the present invention, there is provided a multi-layered secondary battery having high safety when an abnormal temperature rises.

It is sectional drawing of the secondary battery which concerns on a 1st form. It is sectional drawing of the electrode body of the secondary battery which concerns on a 1st form. It is the figure which showed arrangement | positioning of each separator of the secondary battery used for experiment. It is a figure which shows the result of experiment. It is a figure for demonstrating the barrier layer which can cause a shutdown to a cell layer. It is sectional drawing of the secondary battery which concerns on a 2nd form. It is sectional drawing of the electrode body of the secondary battery which concerns on a 2nd form.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a lithium ion secondary battery.

[First embodiment]
FIG. 1 is a cross-sectional view of a secondary battery 100 in this embodiment. As shown in FIG. 1, the secondary battery 100 has a plurality of electrode plates 111 formed by forming a positive electrode active material layer P on the lower surface of the current collector 121 and a negative electrode active material layer N on the opposite upper surface. ing. That is, the secondary battery 100 is a so-called bipolar lithium ion secondary battery. In the uppermost electrode plate 110 in FIG. 1, the positive electrode active material layer P is formed only on the lower surface of the current collector 120. On the other hand, in the lowermost electrode plate 112 in FIG. 1, the negative electrode active material layer N is formed only on the upper surface of the current collector 122.

  Further, the secondary battery 100 of this embodiment has a total of 16 electrode plates including a plurality of electrode plates 111 and an electrode plate 110 located on the uppermost side and an electrode plate 112 located on the lowermost side. doing. And the electrode body 140 of the secondary battery 100 is comprised by laminating | stacking these 16 electrode plates on both sides of the separator S between them. Further, the secondary battery 100 is configured by housing the electrode body 140 in a laminate sheet 150.

  The current collector 120 of the uppermost electrode plate 110 in FIG. 1 is longer to the left than the other current collectors 121 and 122. Furthermore, the left end of the current collector 120 protrudes leftward from the edge of the laminate sheet 150, thereby forming a positive electrode tab 160. Further, the current collector 122 of the lowermost electrode plate 112 in FIG. 1 is longer to the right than the other current collectors 120 and 121. Further, the right end of the current collector 122 protrudes rightward from the edge of the laminate sheet 150 to constitute a negative electrode tab 170.

  The current collectors 120, 121, and 122 are all made of the same material. As the current collectors 120, 121, and 122, for example, a metal foil made of stainless steel (SUS), copper, nickel, titanium, or the like is preferable.

The positive electrode active material layer P contains a positive electrode active material capable of inserting and extracting lithium ions. Examples of the positive electrode active material include lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMnO ₂ ), lithium nickelate (LiNiO ₂ ), and ternary LiNi _1/3 Co _1/3 Mn _1/3 O _2. Is exemplified. In addition to these, those conventionally used in lithium ion secondary batteries can be preferably used.

  The negative electrode active material layer N contains a negative electrode active material that can occlude and release lithium ions. Examples of the negative electrode active material include carbon-based materials, lithium transition metal composite oxides, and lithium transition metal composite nitrides. In addition to these, those conventionally used in lithium ion secondary batteries can be preferably used.

  The separator S is a porous film made of, for example, polyethylene (PE) or polypropylene (PP). As the separator S, a porous film can be used alone. It can also be used as a multilayer structure in which different porous films are alternately laminated. Further, the separator S contains an electrolytic solution obtained by dissolving a lithium salt in an organic solvent.

  The positive electrode active material layer P and the negative electrode active material layer N can be charged / discharged via the electrolyte contained in the separator S therebetween. That is, the separator S and the positive electrode active material layer P and the negative electrode active material layer N adjacent to the separator S constitute a single cell layer. That is, the secondary battery 100 includes an electrode body 140 formed by connecting a plurality of single battery layers electrically in series with each other.

  FIG. 2 is a cross-sectional view of electrode body 140 in the same cross section as that of secondary battery 100 shown in FIG. However, in order to describe the electrode body 140, in FIG. 1 and FIG. As described above, the separator S and the positive electrode active material layer P and the negative electrode active material layer N adjacent to the separator S constitute a single cell layer. Therefore, in FIG. 2, the single cell layers X <b> 1 to X <b> 15 are assigned to the single cell layers from the top to the bottom in the stacking direction (vertical direction in FIG. 2). In the following, the cell layers X1 to X15 will be described as the cell layer X, omitting the numbers in the description that is not particularly distinguished.

  In FIG. 2, the positive electrode active material layer P, the separator S, and the negative electrode active material layer N are assigned the same numbers 1 to 15 as the numbers of the unit cell layers X in which these are arranged. However, the positive electrode active material layer P and the negative electrode active material layer N in this embodiment are the same in all the cell layers X1 to X15 regardless of the assigned numbers. However, the separator S differs depending on the position of the single cell layer X disposed therein. This point will be described in detail later. In addition, hereinafter, the positive electrode active material layer P, the separator S, and the negative electrode active material layer N are also omitted in the description that is not particularly distinguished.

  Further, a sealing member 130 is provided around the unit cell layer X. The sealing member 130 surrounds the periphery of the unit cell layer X without a gap. Thereby, the sealing member 130 prevents the electrolyte from leaking from the separator S. That is, the increase in internal resistance due to the lack of electrolyte in the single cell layer X is suppressed. Furthermore, when the electrolyte solution leaks from the separator S, the so-called liquid junction in which the different cell layers X are short-circuited is prevented.

  Here, in the secondary battery 100, it is preferable that the single battery layer X8 located at least in the center in the stacking direction among the single battery layers X1 to X15 is shut down at the lowest temperature. As described above in paragraph [0005], the shutdown is a function for physically stopping the charge / discharge by increasing the resistance. In this embodiment, at least the single cell layer X8 is shut down at the lowest temperature, so that at least the separator S8 among the separators S1 to S15 has a lower softening point than the other separators S. .

  When the secondary battery 100 is overcharged, the temperature tends to rise toward the center. This is because the center of the secondary battery 100 is less likely to dissipate heat than the outside, and heat tends to be trapped. In the secondary battery 100, the single battery layer X8 is located at the center of the stacking direction among the single battery layers X1 to X15.

  Therefore, in the secondary battery 100 of this embodiment, the separator S8 positioned at least in the center in the stacking direction has a lower softening point than the other separators S. As a result, at least the single cell layer X8 can be shut down at the lowest temperature. Therefore, in the secondary battery 100, when overcharge occurs, this can be stopped, and it can be avoided that a thermal runaway state occurs.

  Further, in the secondary battery 100, it is preferable that at least the softening points of the separators S1 and S15 among the separators S1 to S15 are higher than those of the other separators S. Separators S1 and S15 constitute unit cell layers X1 and X15, respectively. The cell layers X1 and X15 are located on the outermost side in the stacking direction among the cell layers X1 to X15. For this reason, the cell layers X1 and X15 are most susceptible to the external temperature of the secondary battery 100. That is, when the external temperature of the secondary battery 100 becomes high, the temperature is most likely to increase.

  Here, the increase in the external temperature of the secondary battery 100 cannot be stopped by the shutdown. This is because the temperature is not increased due to charging / discharging of the secondary battery 100. Then, when the temperature of the separator S exceeds the softening point, the separator S is completely melted and a hole is formed. This completely melted hole is much larger than the normal pores of the separator S, which is a porous film. In other words, the positive electrode active material layer P and the negative electrode active material layer N may come into contact with each other at the location of the separator S where the hole is completely melted and perforated, and there is a risk of short circuit. That is, when the external temperature of the secondary battery 100 becomes high, the outermost single cell layers X1 and X15 are most likely to be short-circuited.

  Therefore, in the secondary battery 100 of the present embodiment, among the separators S1 to S15, at least the outermost separators S1 and S15 have higher softening points than the other separators S. . Thereby, in the secondary battery 100, it has the structure with high heat resistance with respect to the heating from the outside.

  As described above, in the secondary battery 100 of this embodiment, it is preferable to use separators S1 to S15 having different softening points depending on the arrangement. And it is preferable that the softening point of the separator S8 located at least in the center in the stacking direction is the lowest. Furthermore, it is preferable that the softening point of the separators S1 and S15 located at least on the outermost side in the stacking direction is the highest.

  By the way, the softening point of the separator S can be differentiated by using different materials, for example. Specifically, PE having a softening point of about 130 ° C. can be used alone as a low softening point separator having a low softening point. Further, as a high softening point separator having a high softening point, PP having a softening point of about 160 ° C. can be used alone.

  For example, even if the same material is used, the softening point can be differentiated by using materials having different molecular weights. Specifically, for example, even in the same PE, it is conceivable to use a low softening point separator having a lower molecular weight than that used for a high softening point separator.

  Moreover, as the separator S, a separator having a multilayer structure in which a plurality of porous films of different materials are alternately laminated may be used. Specifically, this is the case when a separator having a PP / PE / PP structure is used. In this case, for example, it is conceivable to use a low softening point separator having a lower molecular weight of the intermediate PE layer than the high softening point separator.

[Confirmation of effect]
In order to confirm the effect of the present invention, the inventors manufactured secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 4, and conducted the following two experiments.
1. Overcharge experiment 2. Heating experiment

  The secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 4 have the same structure as the secondary battery 100. However, in these secondary batteries, only the materials used for the separators S1 to S15 are different. In this experiment, PE having a softening point of about 130 ° C. is used alone as the low softening point separator, and PP having a softening point of about 160 ° C. is used alone as the high softening point separator. That is, each of the secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 4 was manufactured by using PE and PP properly as the separator S.

  FIG. 3 shows the materials of the separators S1 to S15 used in Examples 1 and 2 and Comparative Examples 1 to 4, respectively. As shown in FIG. 3, the secondary batteries of Examples 1 and 2 are secondary batteries that satisfy the conditions of the present embodiment described above. That is, PE (low softening point separator) is used as at least the separator S8. In addition, PP (high softening point separator) is used as at least the separators S1 and S15.

  On the other hand, the secondary batteries of Comparative Examples 1 to 4 are secondary batteries that do not satisfy at least one of the conditions of this embodiment. That is, in the secondary batteries of Comparative Example 1 and Comparative Example 2, separators having the same softening point are used as the separators S1 to S15. In the secondary battery of Comparative Example 1, PP (high softening point separator) is used as the separators S1 to S15. In the secondary battery of Comparative Example 2, PE (low softening point separator) is used as the separators S1 to S15. In the secondary batteries of Comparative Examples 3 and 4, PP (high softening point separator) is used as the separator S8. Furthermore, PE (low softening point separator) is used as the separators S1 and S15.

  Next, “1. Overcharge experiment” performed using these experimental secondary batteries will be described. In this experiment, the secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 4 were overcharged while measuring the temperature until at least one of the separators S1 to S15 was shut down. The temperature of each secondary battery during the overcharge experiment was measured by attaching a temperature sensor to the portion corresponding to the upper center in FIG. Note that the SOC (State of Charge) of each secondary battery at the start of the overcharge experiment was 100% (full charge state). The temperature at the start of the overcharge experiment was 25 ° C. Furthermore, the C rate represented by the ratio of the current value (A) to the full charge capacity (Ah) was overcharged with a current of 10C. And when the voltage of the secondary battery during overcharge became 150V (10V x number of single battery layers) or more, it was set as a judgment condition that the secondary battery was shut down.

  In “2. Heating Experiment”, the secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 4 were measured while measuring the temperature until at least one of the cell layers X1 to X15 was short-circuited. More heated. The temperature of each secondary battery during the heating experiment was measured by attaching a temperature sensor at the same position as in “1. Overcharge experiment” above. Note that the SOC of each secondary battery at the start of the heating experiment was 90%. The temperature at the start of the heating experiment was 25 ° C. Further, each secondary battery was heated by increasing its external temperature at 10 ° C./min. And when the voltage of the secondary battery during heating became 3V or less, it was set as the judgment condition that the short circuit occurred in the secondary battery.

  The results of the overcharge experiment and heating experiment are shown in FIG. In FIG. 4, the horizontal axis represents the temperature at the time of shutdown in the overcharge experiment. The vertical axis represents the temperature at the time of a short circuit in the heating experiment. The results of the secondary batteries of Examples 1 and 2 are indicated by “◯”. The results of the secondary batteries of Comparative Examples 1 to 4 are indicated by “x”.

  As seen on the horizontal axis of FIG. 4, the temperature at the time of shutdown of the secondary batteries of Examples 1 and 2 and Comparative Example 2 is lower than the temperature at the time of shutdown of the secondary batteries of Comparative Examples 1, 3 and 4. That is, at least in the secondary battery using the low softening point separator for the separator S8, the shutdown occurs while the heat generation is small after the overcharge experiment is started. On the other hand, in the secondary battery using the high softening point separator as the separator S8, the temperature is very high when the shutdown occurs. Therefore, it was confirmed that a secondary battery using a low softening point separator for at least the separator S8 tends to be safe when overcharge occurs.

  As seen from the vertical axis of FIG. 4, the temperature when the secondary batteries of Examples 1 and 2 and Comparative Example 1 are short-circuited is higher than the temperature when the secondary batteries of Comparative Examples 2 to 4 are short-circuited. That is, at least in the secondary battery using the high softening point separator for the separators S1 and S15, the heat resistance against external heating is high. On the other hand, in the secondary battery using the low softening point separator for the separators S1 and S15, the heat resistance against external heating is low. Therefore, it was confirmed that at least secondary batteries using high softening point separators S1 and S15 tend to be safe when heated from the outside.

  Moreover, as shown in FIG. 4, in the secondary batteries of Comparative Examples 1 to 4, at least one of the cases where overcharge occurred and the case where the batteries were heated from the outside tended to be unsafe. On the other hand, in the secondary batteries of Examples 1 and 2, there was a safety tendency both when the overcharge occurred and when heated from the outside.

  As described above in detail, the secondary battery 100 of the present embodiment uses a separator having the lowest softening point among the separators S1 to S15 as the separator S8 of the single cell layer X8 located at least in the center in the stacking direction. ing. As a result, among the single cell layers X1 to X15, the single cell layer X8 located at least in the center in the stacking direction can be shut down at the lowest temperature. Moreover, the secondary battery 100 uses the separator with the highest softening point among the separators S1 to S15 for the separators S1 and S15 of the single battery layers X1 and X15 located at least on the outermost side in the stacking direction. Thereby, the heat resistance with respect to the heating from the outside of the secondary battery 100 can be made high. Therefore, a highly safe secondary battery is realized when the abnormal temperature rises.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, in the present embodiment, the present invention is applied to a lithium ion secondary battery, but the present invention can also be applied to other secondary batteries.

  Further, for example, in the present embodiment, since the number of unit cell layers constituting the secondary battery is an odd number, the separator located at the center in the stacking direction is one sheet. However, when the number of unit cell layers constituting the secondary battery is an even number, there are two separators positioned at the center in the stacking direction. In this case, at least one of the two separators located at the center in the stacking direction may be the one having the lowest softening point among the separators used in the secondary battery.

  In this embodiment, the separator is made of a porous film containing an electrolytic solution, but the present invention is not limited to this. A separator having a mesh structure may be used, and a solid electrolyte may be included in the separator. And in the case of this structure, the sealing member for sealing a cell layer is unnecessary.

  Further, in this embodiment, the configuration in which the separator is caused to shut down by the separator is described, but the present invention is not limited to this. The shutdown of the cell layer can be caused by other than the separator. Specifically, as shown in FIG. 5, the barrier layer B is provided on the current collector 121 side of the positive electrode active material layer P constituting the single battery layer X.

  The barrier layer B is composed of a conductive material 1 and a polymer 2 as shown in FIG. Examples of the conductive material 1 include carbon powders such as acetylene black, furnace black, and ketjen black. Examples of the polymer 2 include polymer materials such as polyvinylidene fluoride (PVDF) and polyvinylidene chloride (PVDC).

  In the barrier layer B, a large number of conductive materials 1 are usually in contact with each other. For this reason, the conductive path between the current collector 121 and the positive electrode active material layer P is satisfactorily formed. However, in the barrier layer B in a state where the temperature is excessively increased, the contact between the conductive materials 1 is hindered by the thermal swelling of the polymer 2. For this reason, the resistance between the current collector 121 and the positive electrode active material layer P is excessively increased, and charging / discharging of the unit cell layer X is physically stopped. That is, the single cell layer X is shut down.

  In addition, the temperature at which the barrier layer B is shut down varies depending on the molecular weight of the polymer 2, for example. That is, by using a polymer 2 having a large molecular weight, the temperature at which shutdown occurs in the barrier layer B increases. On the other hand, by using a polymer 2 having a low molecular weight, the temperature at which shutdown occurs in the barrier layer B is lowered.

  And you may make the barrier layer B which has such a shutdown function apply to the secondary battery 100 of this form. That is, the barrier layer B that causes shutdown at the lowest temperature is provided in the single battery layer X8 located at least in the center in the stacking direction. Specifically, it is conceivable to provide a barrier layer B that causes shutdown at a temperature lower than that of all the separators S at least in the single cell layer X8 among the single cell layers X1 to X15. Moreover, the barrier layer B is provided in all the single cell layers X1 to X15, and at least the barrier layer B of the single cell layer X8 is configured to be shut down at a lower temperature than the other barrier layers B and all the separators S. It is possible.

[Second form]
The second embodiment will be described. The secondary battery of this embodiment has a different structure from the secondary battery of the first embodiment. FIG. 6 is a cross-sectional view of the secondary battery 200 in this embodiment. As shown in FIG. 6, the secondary battery 200 includes a positive electrode plate 211 in which a positive electrode active material layer P is formed on both surfaces of a positive electrode current collector 220, and a negative electrode active material layer N on both surfaces of a negative electrode current collector 290. A plurality of formed negative electrode plates 281 are provided. That is, the secondary battery 200 is a so-called monopolar type lithium ion secondary battery. In the positive electrode plate 210 located on the uppermost side in FIG. 6, the positive electrode active material layer P is formed only on the lower surface of the positive electrode current collector 220. On the other hand, in the negative electrode plate 280 located on the lowermost side in FIG. 6, the negative electrode active material layer N is formed only on the upper surface of the negative electrode current collector 290.

  Further, the secondary battery 200 of the present embodiment has a total of eight positive electrode plates including the positive electrode plate 210 located on the uppermost side in addition to the plurality of positive electrode plates 211. Further, in addition to the plurality of negative electrode plates 281, a total of eight negative electrode plates including the lowermost negative electrode plate 280 are provided. The electrode body 240 of the secondary battery 200 is configured by alternately stacking these eight positive plates and eight negative plates while sandwiching the separator S therebetween. In addition, the secondary battery 200 is configured by housing the electrode body 240 in a laminate sheet 250.

  As shown in FIG. 6, each of the positive electrode current collectors 220 is longer to the left than the negative electrode current collector 290. The left end of the positive electrode current collector 220 is connected to the positive electrode tab 260. The positive electrode tab 260 has an end 261 on the side not connected to the positive electrode current collector 220 protruding leftward from the edge of the laminate sheet 250. Further, each of the negative electrode current collector 290 is longer to the right than the positive electrode current collector 220. The right end of the negative electrode current collector 290 is connected to the negative electrode tab 270. The negative electrode tab 270 has an end 271 on the side not connected to the negative electrode current collector 290 protruding rightward from the edge of the laminate sheet 250.

  All of the positive electrode current collectors 220 are made of the same material. Specifically, an aluminum foil is exemplified as a suitable material for the positive electrode current collector 220. Further, the negative electrode current collector 290 is made of the same material. Specifically, a copper foil is exemplified as a suitable material for the negative electrode current collector 290. As the active material contained in each of the positive electrode active material layer P and the negative electrode active material layer N, the same material as in the first embodiment can be used. As the separator S, the same separator as in the first embodiment can be used.

  Also, the same electrolyte solution as in the first embodiment can be used. However, in this embodiment, the electrolytic solution fills the entire inside of the laminate sheet 250. As a result, the separator S contains an electrolytic solution. For this reason, the secondary battery 200 does not have the sealing member 130 like the secondary battery 100 of the first embodiment.

  The positive plates 210 and 211 and the negative plates 280 and 281 can be charged / discharged via the electrolyte contained in the separator S therebetween. That is, also in the secondary battery 200 of this embodiment, the separator S and the positive electrode active material layer P and the negative electrode active material layer N adjacent to the separator S constitute a single cell layer. Therefore, it can be said that the secondary battery 200 includes an electrode body 240 formed by connecting a plurality of single battery layers electrically in parallel with each other.

  7 is a cross-sectional view of electrode body 240 in the same cross section as that of secondary battery 200 shown in FIG. However, for the description of the electrode body 240, in FIG. 6 and FIG. As described above, the separator S and the positive electrode active material layer P and the negative electrode active material layer N adjacent to the separator S constitute a single cell layer. For this reason, in FIG. 7, for each single cell layer, reference numerals of the single cell layers Y1 to Y15 are given from the top to the bottom in the stacking direction (the vertical direction in FIG. 7). In the following, the cell layers Y1 to Y15 are described as the cell layer Y with the numbers omitted in the description that is not particularly distinguished.

  In FIG. 7, the positive electrode active material layer P, the separator S, and the negative electrode active material layer N are also assigned numbers 1 to 15 that are the same as the numbers of the unit cell layers Y in which they are arranged. However, also in this embodiment, the positive electrode active material layer P and the negative electrode active material layer N are the same in all the cell layers Y1 to Y15 regardless of the assigned numbers. However, also in this embodiment, as in the first embodiment, the separator S differs depending on the position of the unit cell layer Y in which the separator S is disposed. Note that the numbers of the positive electrode active material layer P, the separator S, and the negative electrode active material layer N are also omitted in descriptions that are not particularly distinguished.

  And also in the secondary battery 200 of this embodiment, it is preferable that a shutdown occurs at the lowest temperature in the single battery layer Y8 located at least in the center in the stacking direction among the single battery layers Y1 to Y15. For this reason, also in the secondary battery 200, at least the separator S8 among the separators S1 to S15 has a lower softening point than the other separators S.

  Also in the secondary battery 200, when overcharge occurs in the secondary battery 200, the temperature tends to rise toward the center in the stacking direction of the single battery layers Y. For this reason, it is preferable that the single cell layer Y located at the center in the stacking direction is shut down at a lower temperature.

  In the secondary battery 200 of the present embodiment, even if the single battery layer Y among the single battery layers Y1 to Y15 is shut down, the entire charging / discharging of the secondary battery 200 cannot be stopped. This is because in the secondary battery 200, the cell layers Y1 to Y15 are connected in parallel. However, charging / discharging of the unit cell layer Y whose temperature has excessively increased can be stopped. That is, in the secondary battery 200 as well, it can be avoided that this becomes a thermal runaway state due to overcharging.

  Moreover, also in the secondary battery 200 of this embodiment, it is preferable that at least the softening points of the separators S1 and S15 among the separators S1 to S15 are higher than those of the other separators S. This is because the separators S1 and S15 constitute the unit cell layers Y1 and Y15 located on the outermost side in the stacking direction among the unit cell layers Y1 to Y15. That is, when the external temperature of the secondary battery 200 becomes high, the temperature is most likely to increase accordingly. That is, by using at least the separators S1 and S15 having a higher softening point than the other separators S, the secondary battery 200 can be configured to have high heat resistance against heating from the outside. .

  As described above, also in the secondary battery 200 of this embodiment, it is preferable to use separators S1 to S15 having different softening points depending on the arrangement. And it is preferable that the softening point of the separator S8 located at least in the center in the stacking direction is the lowest. Furthermore, it is preferable that the softening point of the separators S1 and S15 located at least on the outermost side in the stacking direction is the highest.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, in the present embodiment, the present invention is applied to a lithium ion secondary battery, but the present invention can also be applied to other secondary batteries.

  Further, for example, in the present embodiment, since the number of unit cell layers constituting the secondary battery is an odd number, the separator located at the center in the stacking direction is one sheet. However, when the number of unit cell layers constituting the secondary battery is an even number, there are two separators positioned at the center in the stacking direction. In this case, at least one of the two separators located at the center in the stacking direction may be the one having the lowest softening point among the separators used in the secondary battery.

  In this embodiment, the separator is made of a porous film containing an electrolytic solution, but the present invention is not limited to this. A configuration in which a mesh-like separator is used and a solid electrolyte is included in the separator may be used.

  Further, in this embodiment, the configuration in which the separator is caused to shut down by the separator is described, but the present invention is not limited to this. The shutdown of the single cell layer may be caused by the barrier layer B described above with reference to FIG.

DESCRIPTION OF SYMBOLS 100 ... Secondary battery 110, 111, 112 ... Electrode plate 120, 121, 122 ... Current collector 140 ... Electrode body N1-N15 ... Negative electrode active material layer P1-P15 ... Positive electrode active material layer S1-S15 ... Separator X1-X15 ... Single cell layer

Claims (3)

Two double-sided electrode plates having a positive electrode active material layer or negative electrode active material layer formed on at least one side of the current collector foil, and two sheets having a positive electrode active material layer or negative electrode active material layer formed on both sides of the current collector foil The above intermediate electrode plate and separator,
The two end electrode plates are positioned at both ends of the stack, the two or more intermediate electrode plates are positioned between the two end electrode plates, and the separator is always sandwiched between the electrode plates; and In a stacked type secondary battery having an electrode body in which a positive electrode active material layer and a negative electrode active material layer face each other across each separator and are stacked in a single cell layer,
The shutdown temperature, which is the temperature at which charging / discharging stops, of the central cell layer group including the cell layer located in the center in the stacking direction and not including the cell layers at both ends,
A laminated secondary battery characterized by being lower than the shutdown temperature of other cell layers. The stacked secondary battery according to claim 1,
The separator included in the central cell layer group has a lower softening point than the separators included in other cell layers. The stacked secondary battery according to claim 1 or 2,
The separator included in the single cell layer group near the both ends including the single cell layer positioned at both ends in the stacking direction and not including the central single cell layer has a higher softening point than the separator included in the other single cell layers. A feature of a stacked type secondary battery.

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