JP2017117624A - Lithium ion secondary battery structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery structure which hardly causes Li precipitation on a negative electrode in a low-temperature environment (for example, a temperature environment at 0°C or lower), and which can reduce a rise in internal resistance of a lithium ion secondary battery in a temperature environment at a normal temperature or higher (for example, 25°C or higher).SOLUTION: A protrusion of a cooling plate 20 comprises: a first protrusion 21 which is arranged at a position facing an electrode body 15 in a direction (a first direction D1) intersecting a lateral face 11b of a battery case 11; and a second protrusion 22 which is arranged at a position not facing the electrode body 15 in the direction (the first direction D1) intersecting the lateral face 11b of the battery case 11. A protrusion amount L1 of the first protrusion 21 and a protrusion amount L2 of the second protrusion 22 are equal to each other in a normal temperature environment. A thermal expansion coefficient of the first protrusion 21 is higher than that of the second protrusion 22.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a lithium ion secondary battery structure.

  Patent Document 1 discloses a lithium ion secondary battery having an electrode body having a positive electrode and a negative electrode, and a rectangular parallelepiped battery case that accommodates the electrode body, a plate-shaped main body, and a surface of the main body A lithium ion secondary battery structure (battery module) comprising: a cooling plate (spacer) having a plurality of protrusions protruding from the battery; and a pair of end plates fixed with the lithium ion secondary battery and the cooling plate interposed therebetween. It is disclosed. The lithium ion secondary battery and the cooling plate are in a state in which the tip of the protruding portion of the cooling plate is in contact with the side surface of the battery case, with a pair of end plates receiving a compressive load in a direction perpendicular to the side surface of the battery case. It is fixed (restrained).

  Thus, by applying a compressive load to the lithium ion secondary battery, the distance between the positive and negative electrodes of the electrode body in the battery case can be reduced, and the internal resistance of the battery can be reduced. Moreover, a lithium ion secondary battery can be cooled by flowing a coolant through a flow path formed between the cooling plate and the side surface of the battery case. In the lithium ion secondary battery structure of Patent Document 1, a plurality of lithium ion secondary batteries are arranged in a direction perpendicular to the side surface of the battery case with a cooling plate interposed therebetween.

JP 2010-92833 A

  In the lithium ion secondary battery structure of Patent Document 1, the lithium ion secondary battery and the pair of end plates sandwiching the lithium ion secondary battery and the cooling plate are fixed by a constraining rod formed of a shape memory alloy. The cooling plate is fixed (restrained) in a state of receiving a compressive load in a direction orthogonal to the side surface of the battery case. And when a part of lithium ion secondary battery overheats, a restraint rod will extend | expand by thermal expansion, and a pair of end plate will displace to the direction which mutually leaves | separates. Thereby, the compressive load is released and an air layer can be formed between the lithium ion secondary battery and the cooling plate. This suppresses the heat of the lithium ion secondary battery that has been overheated from being transmitted to other lithium ion secondary batteries.

  By the way, as described above, the lithium ion secondary battery and the cooling plate are arranged in a direction perpendicular to the side surface of the battery case by the pair of end plates in such a manner that the tip of the protrusion of the cooling plate contacts the side surface of the battery case. When a lithium ion secondary battery is used while being fixed (restrained) under a compressive load, a large amount of Li is charged on the negative electrode surface when charged in a low temperature environment (for example, a temperature environment of 0 ° C. or lower). In some cases, the battery capacity may be greatly reduced. This was more likely to occur as the compression load (restraint load) was larger.

  Specifically, the electrode body in the battery case has a side surface of the battery case formed by a first protrusion disposed at a position facing the electrode body in a direction orthogonal to the side surface of the battery case, of the protrusions of the cooling plate. Pressed through. The first protrusions are arranged with an interval for forming the refrigerant flow path. For this reason, the site | part which opposes a 1st projection part about the direction orthogonal to the side surface of a battery case among an electrode body receives a big pressing force compared with the site | part which does not oppose a 1st projection part. For this reason, variation in the distance between the positive and negative electrodes occurs in the electrode body, which causes variation in charging. This is because Li is more likely to move as the distance between the positive and negative electrodes is smaller.

  Therefore, when charged in a low temperature environment (for example, a temperature environment of 0 ° C. or lower), the amount of Li in the negative electrode has become more uneven, and Li has become excessive (Li cannot be fully inserted). Li may be deposited on the surface of the film. The variation in the distance between the positive and negative electrodes increases as the compressive load (restraint load) in the lithium ion secondary battery structure is increased and the pressing force of the first protrusion on the side surface of the battery case is increased. For this reason, Li precipitation on the negative electrode was more likely to occur as the pressing force of the first protrusion on the side surface of the battery case was increased. For this reason, in order to reduce Li precipitation at the negative electrode, it is preferable to reduce the pressing force of the first protrusion on the side surface of the battery case.

  However, when the lithium ion secondary battery is charged and discharged in a temperature environment of normal temperature or higher (for example, 25 ° C. or higher) by reducing the pressing force on the side surface of the battery case by the first protrusion, The internal resistance of the secondary battery may be greatly increased.

  The present invention has been made in view of the present situation, and Li precipitation is unlikely to occur in the negative electrode in a low temperature environment (for example, a temperature environment of 0 ° C. or lower), and is at room temperature or higher (for example, 25 ° C. or higher). It is an object of the present invention to provide a lithium ion secondary battery structure capable of reducing an increase in internal resistance of the lithium ion secondary battery in a temperature environment.

  According to one embodiment of the present invention, a lithium ion secondary battery including an electrode body having a positive electrode and a negative electrode, and a rectangular parallelepiped battery case that houses the electrode body, a plate-shaped main body portion, and the main body portion A cooling plate having a plurality of protrusions protruding from the surface, and the lithium ion secondary battery and the cooling plate (which is a pair of end plates fixed with the lithium ion secondary battery and the cooling plate sandwiched therebetween) A pair of end plates whose positions are fixed in a state of sandwiching the lithium ion secondary battery and the cooling plate, the tip of the protruding portion of the cooling plate is in contact with the side surface of the battery case The lithium ion secondary battery structure is fixed (constrained) by the pair of end plates while receiving a compressive load in a direction orthogonal to the side surface of the battery case. The protrusion of the cooling plate is orthogonal to the first protrusion disposed at a position facing the electrode body in the direction orthogonal to the side surface of the battery case and the side surface of the battery case. A second protrusion disposed at a position not facing the electrode body with respect to the direction, and a protrusion amount of the first protrusion portion (a protrusion amount from the surface of the main body portion) and a protrusion of the second protrusion portion The amount (the amount of protrusion from the surface of the main body) is equal to each other in a normal temperature environment (for example, a temperature environment of 25 ° C.), and the thermal expansion coefficient (linear expansion coefficient) of the first protrusion is the second protrusion. This is a lithium ion secondary battery structure that has a higher coefficient of thermal expansion (linear expansion coefficient).

  The above-described lithium ion secondary battery structure is a mode in which the tip of the protrusion of the cooling plate is in contact with the side surface of the battery case, and the lithium ion secondary battery and the cooling plate are a pair of end plates fixed to each other. Thus, the lithium ion secondary battery structure is fixed (restrained) in a state of receiving a compressive load in a direction orthogonal to the side surface of the battery case. In this lithium ion secondary battery structure, the protrusion of the cooling plate is arranged in a direction orthogonal to the side surface of the battery case and the first protrusion disposed at a position facing the electrode body in the direction orthogonal to the side surface of the battery case. And a second protrusion disposed at a position not facing the electrode body. And this 1st projection part and the 2nd projection part satisfy the following conditions.

  First, the amount of protrusion of the first protrusion (the amount of protrusion from the surface of the main body) and the amount of protrusion of the second protrusion (the amount of protrusion from the surface of the main body) are in a normal temperature environment (for example, a temperature of 25 ° C. In the environment). Furthermore, the thermal expansion coefficient (linear expansion coefficient) of the first protrusion is higher than the thermal expansion coefficient (linear expansion coefficient) of the second protrusion.

  For this reason, in a temperature environment of room temperature or higher (for example, 25 ° C. or higher), the protruding amount of the first protruding portion is equal to the protruding amount of the second protruding portion (in a free cooling plate not subjected to a compressive load). That's it. Therefore, in a temperature environment of room temperature or higher (for example, 25 ° C. or higher), in the lithium ion secondary battery structure, the force that presses the side surface of the battery case by the first protrusion is the side surface of the battery case by the second protrusion. It becomes larger than the force which presses. For this reason, in a temperature environment of normal temperature or higher (for example, 25 ° C. or higher), the electrode body can be appropriately (sufficiently) pressed by the first protrusion through the side surface of the battery case. Thereby, the rise in the internal resistance of the lithium ion secondary battery when charging / discharging the lithium ion secondary battery in a temperature environment of normal temperature or higher (for example, 25 ° C. or higher) can be reduced.

  On the other hand, in a low-temperature environment (for example, in a temperature environment of 0 ° C. or lower), the first protrusion contracts more than the second protrusion, and the first protrusion (in a free state cooling plate not receiving a compressive load) The protrusion amount of the protrusion is smaller than the protrusion amount of the second protrusion. Thereby, in a low-temperature environment (for example, temperature environment below 0 degreeC), in the lithium ion secondary battery structure, the pressing force to the side surface of a battery case by a 1st projection part can be made small. Thereby, in the direction orthogonal to the side surface of the battery case in the electrode body, the difference between the pressing force to the portion facing the first protrusion and the pressing force to the portion not facing the first protrusion is reduced. Can do.

  Thereby, the variation in the distance between the positive and negative electrodes in the electrode body can be reduced in a low temperature environment (for example, a temperature environment of 0 ° C. or less). Therefore, when a lithium ion secondary battery is charged in a low temperature environment, Li non-uniformity does not easily progress in the negative electrode, and Li does not easily deposit on the surface of the negative electrode active material.

  Note that, in a low temperature environment (for example, in a temperature environment of 0 ° C. or less), the pressing force to the side surface of the battery case by the first protrusion is small, but the pressing force to the side surface of the battery case by the second protrusion is Since it is larger than that, the side surface of the battery case can be appropriately (sufficiently) pressed by at least the second protrusion. Thereby, even in a low temperature environment, the state in which the lithium ion secondary battery and the cooling plate are sandwiched and fixed by the pair of end plates can be appropriately maintained.

The first protrusion may be made of a material having a linear expansion coefficient in the range of 15 to 30 (10 ⁻⁵ / K). Examples of such materials include styrene butadiene rubber (linear expansion coefficient = 23 × 10 ⁻⁵ / K), butyl rubber (linear expansion coefficient = 18 × 10 ⁻⁵ / K), and silicone rubber (linear expansion coefficient = 25 ×). 10 ⁻⁵ / K).

On the other hand, the second protrusion is preferably made of a material having a linear expansion coefficient in the range of 1 to 10 (10 ⁻⁵ / K). Examples of such materials include polypropylene (linear expansion coefficient = 8 × 10 ⁻⁵ / K), polycarbonate (linear expansion coefficient = 7 × 10 ⁻⁵ / K), and polyamide (linear expansion coefficient = 9 × 10 ^−5). / K).

It is a side view of the lithium ion secondary battery structure concerning an embodiment. It is a top view of the lithium ion secondary battery structure. It is BB sectional drawing of FIG. It is CC sectional drawing of FIG. It is a front view of the cooling plate concerning an embodiment. It is a side view of the same cooling plate. It is a figure which shows the internal resistance increase rate by a high temperature cycle charging / discharging test. It is a figure which shows the result of a low-temperature Li precipitation test. 6 is a side view of a cooling plate according to Comparative Example 1. FIG. 6 is a side view of a cooling plate according to Comparative Example 2. FIG. 6 is a cross-sectional view of a lithium ion secondary battery structure according to Comparative Example 1. FIG. 5 is a cross-sectional view of a lithium ion secondary battery structure according to Comparative Example 2. FIG.

Next, an embodiment of the present invention will be described. FIG. 1 is a side view of a lithium ion secondary battery structure 1 according to the present embodiment. FIG. 2 is a top view of the lithium ion secondary battery structure 1. 3 is a cross-sectional view taken along line BB in FIG. 4 is a cross-sectional view taken along the line CC of FIG.
As shown in FIGS. 1 to 4, the lithium ion secondary battery structure 1 includes a lithium ion secondary battery 10, two cooling plates 20, and a pair of end plates 7 and 8.

  Among these, the lithium ion secondary battery 10 includes a flat wound electrode body 15 and a rectangular battery case 11 that accommodates the electrode body 15 (see FIGS. 3 and 4). The electrode body 15 has an oval cross section perpendicular to the winding axis (see FIG. 4), and a sheet-like separator 18 is interposed between the sheet-like positive electrode 16 and the sheet-like negative electrode 17. It is a flat wound electrode body wound around a winding axis.

  In addition, as shown in FIG. 3, the electrode body 15 includes a positive / negative electrode facing portion 15 b where the positive electrode 16 and the negative electrode 17 are opposed to each other with the separator 18 therebetween, and a positive / negative electrode non-facing where the positive electrode 16 and the negative electrode 17 are not opposed. Parts 15c and 15d. The positive / negative electrode non-opposing portion 15c is located at one end portion (lower end portion in FIG. 3) of the electrode body 15, and the positive / negative electrode non-opposing portion 15d is located at the other end portion (upper end portion in FIG. 3) of the electrode body 15. doing. The positive / negative electrode facing portion 15b is located between the positive / negative electrode non-facing portion 15c and the positive / negative electrode non-facing portion 15d. The positive / negative electrode non-opposing portion 15c is a portion where only the positive electrode 16 (specifically, only the positive electrode current collector foil) is wound. Further, the positive / negative electrode non-opposing portion 15d is a portion where only the negative electrode 17 (specifically, only the negative electrode current collector foil) is wound.

  3 and 4, the positive electrode 16 in the electrode body 15 includes a plurality of rectangular positive electrode sheet portions 16b parallel to the first side surface 11b and the second side surface 11c of the battery case 11. . Further, the negative electrode 17 in the electrode body 15 has a plurality of rectangular negative electrode sheet portions 17 b parallel to the first side surface 11 b and the second side surface 11 c of the battery case 11. Furthermore, the separator 18 in the electrode body 15 also includes a plurality of rectangular separator sheet portions 18 b parallel to the first side surface 11 b and the second side surface 11 c of the battery case 11. Therefore, in the electrode body 15, the positive electrode sheet portion 16b and the negative electrode sheet portion 17b are perpendicular to the first side surface 11b and the second side surface 11c of the battery case 11 with the separator sheet portion 18b interposed therebetween (this direction is the first direction). The laminated portion 15f is laminated in one direction D1.

  5 and 6, the cooling plate 20 includes a flat plate-like main body 23 and a plurality of protrusions (four first protrusions 21 and 2) protruding from the surface 23 b of the main body 23. Two second protrusions 22). Of the plurality of protrusions provided on the cooling plate 20, the first protrusion 21 is an electrode in a direction (first direction D1) orthogonal to the first side surface 11b and the second side surface 11c of the battery case 11. It is a protrusion disposed at a position facing the body 15. On the other hand, the 2nd projection part 22 is a projection part arrange | positioned in the position which does not oppose the electrode body 15 about the 1st direction D1 (refer FIG.3 and FIG.4).

  The pair of end plates 7 and 8 is a member made of a metal plate and fixed with the lithium ion secondary battery 10 and the cooling plate 20 in between. In the lithium ion secondary battery structure 1 of the present embodiment, the lithium ion secondary battery 10 and the two cooling plates 20 are arranged such that the tip 21 b of the first protrusion 21 and the tip of the second protrusion 22 of one cooling plate 20. 22b is in contact with the first side surface 11b of the battery case 11, and the tip 21b of the first protrusion 21 and the tip 22b of the second protrusion 22 of the other cooling plate 20 are in contact with the second side 11c of the battery case 11. In this mode, the pair of end plates 7 and 8 are fixed (restrained) in a state where a compressive load is received in the first direction D1 (left and right direction in FIGS. 1 to 4).

  Note that the positions of the end plates 7 and 8 are fixed with the lithium ion secondary battery 10 and the cooling plate 20 sandwiched therebetween. Specifically, the lithium ion secondary battery 10 and the cooling plate 20 are sandwiched between the end plates 7 and 8 in a normal temperature environment (specifically, a temperature environment of 25 ° C.), and in the first direction D1 with respect to them. The end plates 7 and 8 and the lithium ion secondary battery 10 and the cooling plate 20 sandwiched between the four end plates 7 and 8 and a fixed compression load (specifically, a load in the range of 10 to 1000 kgf) The bolt 3 and the nut 5 are used for fastening.

  The end plates 7 and 8 are formed with through holes (not shown) through which the shafts of the bolts 3 can be inserted at the four corners. In the present embodiment, a specified compressive load (specifically, the lithium ion secondary battery 10 and the cooling plate 20 are sandwiched between the end plates 7 and 8 under a normal temperature environment (specifically, a temperature environment of 25 ° C.). Is a state in which a load within the range of 10 to 1000 kgf is applied, and while maintaining this state, the shaft of the bolt 3 is inserted through the through holes of the end plates 7 and 8, and the nut 5 Are screwed together to fix the end plates 7 and 8. Accordingly, the positions of the end plates 7 and 8 are fixed, and the end plates 7 and 8 cause the lithium ion secondary battery 10 and the cooling plate 20 to receive a compressive load in the first direction D1. .

  In FIG. 5, a region A1 facing the electrode body 15 in the first direction D1 is indicated by a broken line. Further, in the first direction D1, a region A2 of the electrode body 15 that faces the positive and negative electrode facing portion 15b is indicated by a two-dot chain line. As shown in FIG. 5, in the present embodiment, the four first projecting portions 21 are all arranged at positions facing the positive and negative electrode facing portions 15 b of the electrode body 15. Therefore, in the lithium ion secondary battery structure 1 of the present embodiment, the positive and negative electrodes of the electrode body 15 are passed through the first side surface 11b and the second side surface 11c of the battery case 11 by the four first protrusions 21 of the cooling plate 20. The facing portion 15b is pressed (compressed) in the first direction D1 (see FIGS. 3 and 4). Thereby, the distance between the positive electrode 16 and the negative electrode 17 can be reduced, and the internal resistance of the lithium ion secondary battery 10 can be reduced.

  Moreover, in the cooling plate 20 of this embodiment, as shown in FIG. 5, the 1st projection part 21 and the 2nd projection part 22 have comprised the elongate shape extended linearly in the up-down direction, and are formed in the left-right direction (1st The projections 21 and the second projections 22 are arranged in parallel with a gap therebetween in a direction orthogonal to the extending direction of the projections 21 and the second projection 22 (which coincides with the winding axis direction of the electrode body 15). For this reason, in the lithium ion secondary battery structure 1, the coolant is vertically moved between the first protrusions 21 or the second protrusions 22 adjacent in the winding axis direction (vertical direction in FIG. 3) of the electrode body 15. Can flow. Specifically, in the lithium ion secondary battery structure 1, the refrigerant flow path P for cooling the lithium ion secondary battery 10 includes the first side surface 11 b of the battery case 11, the main body portion 23 of the cooling plate 20, and The first projection 21 or the second projection 22 is surrounded (see FIG. 3). By circulating the refrigerant through the flow path P, the lithium ion secondary battery 10 constituting the lithium ion secondary battery structure 1 can be cooled.

  Conventionally, as described above, the lithium ion secondary battery and the cooling plate are subjected to a compressive load in a direction perpendicular to the side surface of the battery case in such a manner that the tip of the protrusion of the cooling plate contacts the side surface of the battery case. In a lithium ion secondary battery structure fixed (restrained) in a hot state, a large amount of Li is deposited on the negative electrode surface when the lithium ion secondary battery is charged in a low temperature environment (temperature environment of 0 ° C. or lower). However, this may cause a significant decrease in battery capacity. This was more likely to occur as the compression load (restraint load) was increased.

  Specifically, the electrode body in the battery case has a side surface of the battery case formed by a first protrusion disposed at a position facing the electrode body in a direction orthogonal to the side surface of the battery case, of the protrusions of the cooling plate. Pressed through. The first protrusions are arranged with an interval for forming the refrigerant flow path. For this reason, the site | part which opposes a 1st projection part about the direction orthogonal to the side surface of a battery case among an electrode body receives a big pressing force compared with the site | part which does not oppose a 1st projection part. For this reason, variation in the distance between the positive and negative electrodes occurs in the electrode body, which causes variation in charging. This is because as the distance between the positive and negative electrodes is shorter, Li moves more easily.

  Accordingly, when a lithium ion secondary battery is charged in a low temperature environment (temperature environment of 0 ° C. or lower), the amount of Li in the negative electrode is increased and Li is excessive (Li cannot be inserted). In some cases, Li was deposited on the surface of the negative electrode active material. The variation in the distance between the positive and negative electrodes increases as the compressive load (restraint load) in the lithium ion secondary battery structure is increased and the pressing force of the first protrusion on the side surface of the battery case is increased. For this reason, Li precipitation on the negative electrode was more likely to occur as the pressing force of the first protrusion on the side surface of the battery case was increased. For this reason, in order to reduce Li precipitation at the negative electrode, it can be said that it is preferable to reduce the pressing force of the first protrusion on the side surface of the battery case.

  However, when the lithium ion secondary battery is charged and discharged in a temperature environment of normal temperature or higher (25 ° C. or higher) by reducing the pressing force of the first protrusion on the side surface of the battery case, the lithium ion secondary battery There was a possibility that the internal resistance of the battery would greatly increase.

On the other hand, in this embodiment, the 1st projection part 21 and the 2nd projection part 22 of the cooling plate 20 satisfy | fill the following conditions.
First, the protrusion amount L1 of the first protrusion 21 (the protrusion dimension from the surface 23b of the main body 23, see FIG. 6) and the protrusion amount L2 of the second protrusion 22 (the protrusion dimension from the surface 23b of the main body 23). ) Are equal to each other in a normal temperature environment (25 ° C. temperature environment). Furthermore, the thermal expansion coefficient (linear expansion coefficient) of the first protrusion 21 is higher than the thermal expansion coefficient (linear expansion coefficient) of the second protrusion 22.

In the present embodiment, the first protrusion 21 is made of styrene butadiene rubber (linear expansion coefficient = 23 × 10 ⁻⁵ / K). The second protrusion 22 is made of polypropylene (linear expansion coefficient = 8 × 10 ⁻⁵ / K). The main body 23 is also made of polypropylene (linear expansion coefficient = 8 × 10 ⁻⁵ / K).

  For this reason, under a temperature environment of room temperature or higher (25 ° C. or higher), the protruding amount L1 of the first protruding portion 21 is equal to the protruding amount L2 of the second protruding portion 22 in the free cooling plate 20 that is not receiving a load. That's it. Therefore, in the lithium ion secondary battery structure 1 of the present embodiment, the battery case is formed by the first protrusion 21 with a larger pressing force than the second protrusion 22 in a temperature environment of room temperature or higher (25 ° C. or higher). 11 first side face 11b and second side face 11c can be pressed. Therefore, under a temperature environment of room temperature or higher (25 ° C. or higher), the electrode body 15 (more specifically, in the first direction D1 through the first side surface 11b and the second side surface 11c of the battery case 11 by the first protrusion 21. Specifically, the positive and negative electrode facing portions 15b) can be sufficiently pressed (compressed). Thereby, an increase in the internal resistance of the lithium ion secondary battery 10 when the lithium ion secondary battery 10 is charged and discharged in a temperature environment of room temperature or higher (25 ° C. or higher) can be reduced.

  On the other hand, in a low temperature environment (a temperature environment of 0 ° C. or lower), the first protrusion 21 contracts more than the second protrusion 22, and the first protrusions are in the free state cooling plate 20 not receiving a load. The protrusion amount L1 of 21 is smaller than the protrusion amount L2 of the second protrusion 22. Therefore, in the lithium ion secondary battery structure 1 of the present embodiment, to the first side surface 11b and the second side surface 11c of the battery case 11 by the first protrusion 21 in a low temperature environment (a temperature environment of 0 ° C. or less). The pressing force can be reduced. As a result, the pressing force applied to the portion of the electrode body 15 (more specifically, the positive / negative electrode facing portion 15b) facing the first protrusion 21 in the first direction D1 does not face the first protrusion 21. The difference with the pressing force to the part can be reduced.

  Thereby, the variation in the distance between the positive electrode 16 and the negative electrode 17 in the electrode body 15 (more specifically, the positive and negative electrode facing portion 15b) is reduced in a low temperature environment (a temperature environment of 0 ° C. or less). Can do. Therefore, when a lithium ion secondary battery is charged in a low temperature environment, Li non-uniformity hardly progresses in the negative electrode 17, and Li does not easily deposit on the surface of the negative electrode active material.

  Note that, under a low temperature environment (a temperature environment of 0 ° C. or lower), the pressing force to the first side surface 11b and the second side surface 11c of the battery case 11 by the first protruding portion 21 is small, but the second protruding portion 22 Since the pressing force to the first side surface 11b and the second side surface 11c of the battery case 11 is larger than this, the first side surface 11b and the second side surface 11c of the battery case 11 are appropriately (sufficiently) secured by at least the second protrusion 22. Can be pressed). Thereby, even in a low-temperature environment, the state in which the lithium ion secondary battery 10 and the cooling plate 20 are sandwiched and fixed by the pair of end plates 7 and 8 can be appropriately maintained.

Example 1
In the first embodiment, the lithium ion secondary battery 10 and the cooling plate 20 are sandwiched between the end plates 7 and 8 in a normal temperature environment (specifically, a temperature environment of 25 ° C.), and in the first direction D1 The end plates 7 and 8 and the lithium ion secondary battery 10 and the cooling plate 20 sandwiched between the end plates 7 and 8 were fastened using four bolts 3 and nuts 5 in a state where a compression load (constraint load) of 100 kgf was applied thereto. . Thus, in a normal temperature environment (specifically, a temperature environment of 25 ° C.), the end plates 7 and 8 cause the lithium ion secondary battery 10 and the cooling plate 20 to compress in a first direction D1 by 100 kgf (restraint). A lithium ion secondary battery structure 1 fixed in a state of receiving a load) was produced.

(Comparative Example 1)
As Comparative Example 1, a lithium ion secondary battery structure 201 (see FIG. 11) that is different from the lithium ion secondary battery structure 1 of Example 1 only in the cooling plate was produced. As shown in FIG. 9, the cooling plate 220 of the first comparative example has only the second protrusion 222 as the protrusion, and does not have the first protrusion. That is, the cooling plate 220 of Comparative Example 1 does not have the first protrusions disposed at positions facing the electrode body 15 in the first direction D1, and is disposed at positions not facing the electrode body 15 in the second direction. Only the protrusion 222 is provided (see FIG. 11). In addition, the 2nd protrusion part 222 is a protrusion part equivalent to the 2nd protrusion part 22 of Example 1. FIG.

(High-temperature cycle charge / discharge test)
First, the internal resistance (specifically, the IV resistance value) of the lithium ion secondary battery 10 was measured for the lithium ion secondary battery structures of Example 1 and Comparative Example 1 described above. Specifically, each lithium ion secondary battery 10 was adjusted to SOC 60% under a temperature environment of 25 ° C., and then discharged at a constant current value I of 60 A for 10 seconds. At this time, the battery voltage value before and after the discharge was measured, and the battery voltage drop amount ΔV due to this discharge was calculated. Based on this measurement result, the IV resistance value R of each lithium ion secondary battery 10 was calculated. Specifically, the IV resistance value R (IV resistance value before cycle charge / discharge) of each lithium ion secondary battery 10 was calculated using an arithmetic expression of R = ΔV / I.

  Thereafter, each of the lithium ion secondary battery structures was subjected to cycle charge / discharge in a temperature environment of room temperature or higher (specifically, a temperature environment of 60 ° C.). Specifically, these lithium ion secondary battery structures were subjected to a plurality of charge / discharge cycles within a range of SOC 0% to 100% at a constant current of 2C under a temperature environment of 60 ° C.

  Thereafter, for these lithium ion secondary battery structures, the internal resistance (IV resistance value after cycle charge / discharge) of the lithium ion secondary battery 10 was measured as described above. And about these lithium ion secondary battery structures, the resistance increase rate by cycle charging / discharging was computed. Specifically, it was calculated as resistance increase rate = (IV resistance value after cycle charge / discharge) / (IV resistance value before cycle charge / discharge). The result is shown in FIG.

  As shown in FIG. 7, in Comparative Example 1, the resistance increase rate was 1.07. That is, the internal resistance (IV resistance value) of the lithium ion secondary battery 10 increased by 7% due to cycle charge and discharge. On the other hand, in Example 1, the resistance increase rate was 1.04. That is, the increase rate of the internal resistance (IV resistance value) of the lithium ion secondary battery 10 due to cycle charge / discharge was 4%, and the increase rate of the internal resistance could be reduced by 3% compared to Comparative Example 1. From this result, the lithium ion secondary battery structure 1 of Example 1 is a lithium ion secondary battery when the lithium ion secondary battery 10 is charged and discharged in a temperature environment of room temperature or higher (25 ° C. or higher). 10 can be said to be a lithium ion secondary battery structure capable of reducing the increase in internal resistance of 10.

  The reason can be considered as follows. In Comparative Example 1, as the cooling plate, the cooling plate 220 having only the second protrusions 222 and not having the first protrusions was used. For this reason, the electrode body 15 (more specifically, the positive / negative electrode facing portion 15b) is placed in the first direction D1 through the first side surface 11b and the second side surface 11c of the battery case 11 during the above-described cycle charge / discharge period. It was not possible to sufficiently press (compress). For this reason, it is thought that the internal resistance of the lithium ion secondary battery 10 significantly increased due to the cycle charge / discharge.

  On the other hand, in Example 1, as the cooling plate, the protruding amount L1 of the first protruding portion 21 and the protruding amount L2 of the second protruding portion 22 are equal to each other in a normal temperature environment (25 ° C. temperature environment), Furthermore, the cooling plate 20 in which the first protrusion 21 is made of a material having a higher coefficient of thermal expansion (linear expansion coefficient) than that of the second protrusion 22 is used. Therefore, under a temperature environment of room temperature or higher (25 ° C. or higher), the electrode body 15 (more specifically, in the first direction D1 through the first side surface 11b and the second side surface 11c of the battery case 11 by the first protrusion 21. Specifically, the positive and negative electrode facing portions 15b) were sufficiently pressed (compressed). Thereby, it is considered that the increase in the internal resistance of the lithium ion secondary battery 10 when charging / discharging the lithium ion secondary battery 10 under a temperature environment of room temperature or higher could be reduced.

(Comparative Example 2)
In addition, as Comparative Example 2, a lithium ion secondary battery structure 301 (see FIG. 12) that is different from the lithium ion secondary battery structure 1 of Example 1 only in the cooling plate was manufactured. The cooling plate 320 (see FIG. 10) of the comparative example 2 is different from the cooling plate 20 of the first embodiment only in the material of the first protrusions, and the others are the same. Specifically, each of the first protrusions 321 of the cooling plate 320 of Comparative Example 2 is made of polypropylene (linear expansion coefficient = 8 × 10 ⁻⁵ / K), like the second protrusions 322. ing. Therefore, in the lithium ion secondary battery structure 301 of Comparative Example 2, the first protrusion 321 disposed at a position facing the electrode body 15 and the position not facing the electrode body 15 in the first direction D1. The second protrusions 322 are the same.

(Low-temperature Li precipitation test)
The lithium ion secondary battery structures of Example 1 and Comparative Example 2 were repeatedly subjected to high rate charging in a low temperature environment of 0 ° C. or lower (specifically, a temperature environment of −10 ° C.), and Li deposition in the negative electrode The difficulty of occurrence was investigated.

  Specifically, in a temperature environment of −10 ° C., the lithium ion secondary battery 10 of each lithium ion secondary battery structure is adjusted to an SOC of 80%, and then first, at a constant current of 50 A, constant. Charge for hours. Thereafter, the SOC is returned to 80% (discharged), and charging is performed again at a constant current of 50 A for a certain period of time. After repeating this high rate charging a predetermined number of times, each lithium ion secondary battery 10 was examined for whether Li was deposited on the negative electrode. When Li is not deposited on the negative electrode, the charging current value is increased by 5 A (that is, the charging current value is 55 A), and high rate charging is repeated a predetermined number of times as described above. Regarding the battery 10, it was investigated whether Li was deposited on the negative electrode. In this way, for each lithium ion secondary battery 10, the charging current value was increased by 5 A each time until Li was deposited on the negative electrode, and high-rate charging was repeated. The result is shown in FIG.

As shown in FIG. 8, in Comparative Example 2, Li was not deposited on the negative electrode when charged at a constant current of 70 A, but Li was deposited on the negative electrode when charged at a constant current of 75 A. . On the other hand, in Example 1, even when charging was performed at a constant current of 75 A, Li did not precipitate on the negative electrode. However, when charging was performed at a constant current of 80 A, Li was deposited on the negative electrode.
From this result, the lithium ion secondary battery structure 1 of Example 1 in the negative electrode in a low-temperature environment (under a temperature environment of 0 ° C. or lower) is better than the lithium ion secondary battery structure 301 of Comparative Example 2. It can be said that it is a lithium ion secondary battery structure in which Li precipitation is unlikely to occur.

  The reason can be considered as follows. In the lithium ion secondary battery structure 301 of Comparative Example 2, the first protrusion 321 disposed at a position facing the electrode body 15 and the first position D1 disposed at a position not facing the electrode body 15 in the first direction D1. The cooling plate 320 formed of a material (specifically, polypropylene) having the same thermal expansion coefficient (linear expansion coefficient) as the two protrusions 322 was used. For this reason, the first side surface 11b and the second side surface 11c of the battery case 11 are pressed by the first protrusion 321 with a pressing force equivalent to that of the second protrusion 322 even in a low temperature environment (temperature environment of 0 ° C. or less). Will be.

  On the other hand, in the lithium ion secondary battery structure 1 of Example 1, the cooling plate 20 in which the first protrusion 21 is made of a material having a higher thermal expansion coefficient (linear expansion coefficient) than the second protrusion 22 is used. Yes. For this reason, the first protrusion 21 contracts more greatly than the second protrusion 22 under a low temperature environment (under a temperature environment of 0 ° C. or lower). The first side surface 11 b and the second side surface 11 c of the battery case 11 are pressed by the part 321. Therefore, in Example 1, compared with Comparative Example 2, it can be said that the pressing force to the first side surface 11b and the second side surface 11c of the battery case 11 by the first protrusion 21 can be reduced.

  Thereby, in Example 1, compared with Comparative Example 2, in the low temperature environment (under the temperature environment of 0 ° C. or less), the first electrode body 15 (more specifically, the positive and negative electrode facing portion 15b) is the first. It is considered that the difference between the pressing force applied to the portion facing the first protrusion in the direction D1 and the pressing force applied to the portion not facing the first protrusion can be reduced. For this reason, in Example 1, compared with Comparative Example 2, the distance between the positive electrode 16 and the negative electrode 17 in the electrode body 15 (positive and negative electrode facing portion 15b) in a low-temperature environment (temperature environment of 0 ° C. or less). It is thought that the variation in the size was reduced. Therefore, in Example 1, when the lithium ion secondary battery is charged in a low temperature environment as compared with Comparative Example 2, Li non-uniformity is less likely to proceed in the negative electrode 17, and Li is present on the surface of the negative electrode active material. It is thought that precipitation became difficult.

In the above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the above embodiments, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.
For example, in the embodiment, the first protrusion 21 and the second protrusion 22 of the cooling plate 20 have an elongated shape that extends linearly in the vertical direction (see FIG. 5), but the first protrusion and the second protrusion It is good also as an elongate shape extended linearly in the left-right direction (winding-axis direction of the electrode body 15). Moreover, the shape of the 1st projection part and the 2nd projection part is not restricted to the elongate shape extended linearly, Any shape may be sufficient.

In the embodiment, the first protrusion of the cooling plate is the first protrusion 21 formed of styrene butadiene rubber (linear expansion coefficient = 23 × 10 ⁻⁵ / K). However, the material constituting the first protrusion is not limited to this. For example, butyl rubber (linear expansion coefficient = 18 × 10 ⁻⁵ / K) or silicone rubber (linear expansion coefficient = 25 × 10 ^−5). / K) or the like. The first protrusion is preferably made of a material having a linear expansion coefficient in the range of 15 to 30 (10 ⁻⁵ / K).

In the embodiment, the second protrusion of the cooling plate is the second protrusion 22 formed of polypropylene (linear expansion coefficient = 8 × 10 ⁻⁵ / K). However, the material constituting the second protrusion is not limited to this, and examples thereof include polycarbonate (linear expansion coefficient = 7 × 10 ⁻⁵ / K) and polyamide (linear expansion coefficient = 9 × 10 ⁻⁵ / K). K) or the like. The second protrusion is preferably made of a material having a linear expansion coefficient in the range of 1 to 10 (10 ⁻⁵ / K).

  In the embodiment, the electrode body is a flat wound type wound around the winding axis so that the sheet-like separator 18 is interposed between the sheet-like positive electrode 16 and the sheet-like negative electrode 17. The electrode body 15 was illustrated (refer FIG. 4). However, the form of the electrode body is not limited to this, and, for example, the sheet-like separator 18 is interposed between the sheet-like positive electrode 16 and the sheet-like negative electrode 17, and these are arranged in the first direction D1. Alternatively, a stacked electrode body may be stacked.

1, 201, 301 Lithium ion secondary battery structure 3 Bolt 5 Nut 7, 8 End plate 10 Lithium ion secondary battery 11 Battery case 11b First side surface 11c Second side surface 15 Electrode body 15b Positive and negative electrode facing portions 15c, 15d Positive Negative electrode non-facing portion 16 Positive electrode 17 Negative electrode 18 Separators 20, 220, 320 Cooling plates 21, 221, 321 First protrusions 22, 222, 322 Second protrusions 23, 223, 323 Body D1 First direction (battery case Direction perpendicular to the side)
L1 Projection amount of the first projection L2 Projection amount of the second projection

Claims (1)

A lithium ion secondary battery having an electrode body having a positive electrode and a negative electrode, and a rectangular parallelepiped battery case containing the electrode body;
A cooling plate having a flat plate-shaped main body, and a plurality of protrusions protruding from the surface of the main body;
A pair of end plates whose positions are fixed in a state of sandwiching the lithium ion secondary battery and the cooling plate,
The lithium ion secondary battery and the cooling plate are in a mode in which a tip of the protruding portion of the cooling plate is in contact with a side surface of the battery case, and a direction orthogonal to the side surface of the battery case by the pair of end plates. In a lithium ion secondary battery structure that is fixed in a state of receiving a compressive load,
The protrusion of the cooling plate is
A first protrusion disposed at a position facing the electrode body in a direction perpendicular to the side surface of the battery case;
A second protrusion disposed at a position not facing the electrode body in a direction orthogonal to the side surface of the battery case;
The protruding amount of the first protruding portion and the protruding amount of the second protruding portion are equal to each other under a normal temperature environment,
The lithium ion secondary battery structure has a higher coefficient of thermal expansion of the first protrusion than the coefficient of thermal expansion of the second protrusion.

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