JP2012174571A - Battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heating type battery pack that is constituted by the combination of a plurality of unit cells, improves heat conduction between the unit cells, and can achieves the stable operation.SOLUTION: The battery pack is housed in a housing so as to be constituted by the combination of a plurality of unit cells, and operated at a temperature higher than a room temperature. In the battery pack, a case that constitutes the unit cell includes a plane facing another adjacent unit cell, and adjacent unit cells are assembled in a state in which the planes come into contact with each other. Specifically, the battery pack can be applied to a molten salt battery that uses a molten salt that melts at a temperature higher than a room temperature, as an electrolyte.

Description

  The present invention relates to an assembled battery structure that can be operated at a temperature higher than room temperature, and more particularly to an assembled battery structure that is suitable for a molten salt battery.

Development of relatively large secondary batteries used for power storage, automobiles, and the like is underway. In order to obtain a desired voltage and a desired capacity, an assembled battery in which a plurality of unit cells are combined in series and parallel to form an integrated type is used. Lithium ion batteries, nickel metal hydride batteries, and the like are used at room temperature. However, since heat generated by charging and discharging causes deterioration of battery performance, various means for cooling the entire assembled battery or individual unit cells have been considered. . For example, Patent Document 1 discloses a lithium secondary battery that uses an air-cooled spacer having corrugations such as corrugations and rectangles on its side surface. Patent Document 2 discloses an assembled battery assembled using a frame having a structure for introducing a refrigerant into the assembled battery.
On the other hand, a sodium-sulfur battery is known as a heating type battery that operates by heating to a temperature higher than room temperature. Such a battery has a structure in which a plurality of sodium-sulfur single cells are assembled and accommodated in a heat insulating container, and is operated at a high temperature of about 300 ° C. Due to safety problems, each cell is filled with sand or the like to prevent local abnormal heating or leakage of the active material (Patent Document 3).

Japanese Patent Laid-Open No. 10-112301 Japanese Patent No. 4062273 JP 2000-215908 A

As described above, when forming a battery pack in a conventional secondary battery, it is necessary to prevent abnormal heating or keep the temperature during operation low. For this reason, a cooling structure or a heat insulating structure is provided between the unit cells so that heat does not accumulate between the unit cells constituting the assembled battery or heat does not spread.
The present inventors have developed a molten salt battery that operates at a temperature of 100 ° C. or less and has high safety during overheating. Such a molten salt battery is used as an electrolyte by heating a solid salt at a relatively low temperature to a molten salt at room temperature. For this reason, it is necessary to operate | move, maintaining a electrolyte in a molten state by providing a heating means. Moreover, in order to make it into an operation state from the time of an operation stop, it is calculated | required to heat to operation temperature as soon as possible. Heating means may be provided for each individual unit cell, but this is not preferable because the overall size of the assembled battery increases and the cost increases. Furthermore, when a temperature difference occurs between a portion close to the heating means and a portion far from the heating means, the temperature of the molten salt that is the electrolytic solution varies. As a result, it was found that the internal resistance of the battery is non-uniform, and the characteristics are deteriorated and the life is shortened due to load distribution such that an excessive current flows only in a specific battery. Further, when the temperature distribution is large, there is a possibility that the molten salt of some batteries may solidify or undergo thermal decomposition.

  The present invention has been made in view of such circumstances, and an object of the present invention is to improve the heat conduction between the unit cells in a heating type assembled battery obtained by combining a plurality of unit cells, and to stabilize the unit cell. Another object of the present invention is to provide an assembled battery that can realize the above operation.

  In order to achieve the above object, the assembled battery of the present invention is a assembled battery in which a plurality of unit cells are combined and housed in a housing and operated at a temperature higher than room temperature, and the unit cell is formed. However, it has a plane opposite to the other adjacent unit cells, and the adjacent unit cells are assembled in a state where the planes are in close contact with each other. 1). According to the present invention, since the heat conduction between the unit cells is improved, the temperatures of the adjacent unit cells are easily balanced, and as a result, the temperature of the entire assembled cell is easily stabilized uniformly. For this reason, there are effects such as improvement in battery life, reduction in battery rise time, and improvement in rate characteristics (the entire electrolyte operates well and current density can be increased). Here, the close contact means a state in which the surfaces are in contact with each other without a noticeable gap in a normal sense, in other words, in a state in which the fluid does not easily flow between the surfaces. is there. That is, in contrast to the degree of adhesion, the cooling medium and the air are configured to easily flow between the unit cells for the purpose of cooling in other batteries that are mainly used at room temperature. Therefore, it is interpreted in line with the intention of improving heat conduction by intentionally contacting surfaces.

  In particular, the effect of the present invention is remarkably preferable when the unit cell is a molten salt battery in which a molten salt that melts at a temperature higher than room temperature is used as an electrolyte. In particular, in a molten salt battery provided with an electric heater inside, the temperature in the molten salt battery tends to be non-uniform because the portion near the electric heater becomes high temperature and the far portion becomes low temperature. In general, the higher the temperature, the higher the conductivity of the molten salt. Therefore, the higher the temperature, the higher the output performance of the molten salt battery, for example. When the molten salt battery is used in a state in which the internal temperature is not uniform, the lower one of the internal temperatures greatly affects the performance of the molten salt battery. In addition, the high temperature portion in the battery module is likely to be overcharged or overdischarged, and the high temperature portion is quickly deteriorated. By improving the heat conduction between the unit cells as in the present invention and stabilizing the temperature of the entire assembled battery uniformly, the efficiency of the entire molten salt battery can be increased and the life can be extended.

  It is preferable that the material of the unit cell case is metal, and the surface roughness Ra of the surface to be adhered is 5 μm or less. In order to increase the effect of heat conduction between the unit cells, the case is preferably made of metal, and aluminum and magnesium are particularly preferably used in consideration of the requirement for weight reduction of the case and corrosion resistance. It is preferable to increase the processing accuracy of the flat surface so that the surfaces of the unit cells are in close contact with each other. As a result, the surface roughness Ra is preferably processed to 5 μm or less from the viewpoint of adhesion.

  It is preferable that the unit cell case has a substantially rectangular parallelepiped shape and has an electrode on a surface different from the surface to be adhered. In the configuration of the assembled battery, the unit cell needs an electrode for connecting each other in series or in parallel, a coupling mechanism for fixing them to each other, and the like. In addition to the terminals, there may be a slightly raised portion such as a protrusion such as a pressure valve, a case lid meshing or a welded portion. It is preferable to make such a protrusion not have a structure on a surface that is in close contact with an adjacent unit cell. In particular, since the electrode requires wiring or the like to be connected to the outside, it is difficult to form a close contact structure when it exists on the close contact surface side. Most preferably, a structure that does not provide anything on the surface to be in contact is good, but even if there is a protrusion, it is a structure that fits to each other, or a structure that avoids the protrusion, so that the surface to be in contact is sufficient It may be a structure that can be secured to Here, the term “substantially rectangular parallelepiped” means that it is a rectangular parallelepiped as a whole, but details such as the terminal portion and the lid portion are not flat and are not a strict rectangular parallelepiped.

  Furthermore, it is preferable that the casing has a pressurizing means for pressurizing the unit cell in a direction in which the unit cell is in close contact. This is because the adhesion effect is enhanced. The case includes a case where the case itself has a pressurizing means as a part of its structure. In addition, as described above, the effect of adhesion is easily exhibited when a heater for heating the unit cell is provided (claim 6). The heater is not particularly limited, but a plate-shaped heater is easy to configure, and a plurality of heaters are easily installed in the assembled battery so as to be parallel to the side surface of the unit cell (for example, the largest surface and the vertical surface). Examples of the heater include a ceramic heater.

  As a specific configuration form of the present invention as described above, a case forming a unit cell has a substantially rectangular parallelepiped shape, n unit cells are connected in series, and m sets of unit cells connected in series are arranged in parallel. The case of the unit cells connected in series and / or the case of the set of unit cells connected in parallel are assembled in a state in which their adjacent surfaces are in close contact with each other, An assembled battery provided with at least one heating means is provided between the set of m unit cells connected in parallel (Claim 7).

  ADVANTAGE OF THE INVENTION According to this invention, in the heating type assembled battery which combines a several unit cell, there exists an outstanding effect that heat conduction between unit cells is improved and stable operation | movement can be implement | achieved.

It is a perspective view explaining the whole structure as an example of the assembled battery which concerns on this invention. It is the figure which showed typically the cross section cut in the A-A 'part of FIG. It is a figure explaining the structure of the unit assembled battery used for FIG. 1 as an example of the assembled battery which concerns on this invention. It is a figure which shows the structure of the molten salt battery as an example of the unit cell used for the assembled battery of this invention, A is a top view which shows typically the internal structure of a molten salt battery, B is the longitudinal cross-sectional view.

  The present invention will be described below with reference to the drawings showing embodiments thereof. FIG. 1 is a perspective view illustrating the entire structure of the assembled battery according to the present invention, and a part of the assembled battery is expressed in order to explain the inside. FIG. 1 is a configuration example of an assembled battery in which nine unit assembled batteries each having four unit cells connected in series are connected in parallel. In FIG. 1, nine unit assembled batteries 1 are accommodated in a housing 2 constituting the assembled battery 10. The unit assembled battery 1 has a rectangular parallelepiped shape, and terminals for charging and discharging are formed on the side surfaces of both ends. In this example, the size of the housing 2 is 700 × 280 × 420 mm. The nine unit assembled batteries 1 are arranged in parallel, fixed to the connection terminal plates 4a and 4b by bolts 5 and electrically connected in parallel. The connection terminal plate has a structure in which an end thereof is drawn out of the housing 2, and the connection terminal plate 4a is used as a positive electrode and the connection terminal plate 4b is used as a negative electrode. Each unit assembled battery 1 is heated by a plurality of heaters 3. The heater is energized by an external wiring (not shown), and heats the assembled battery 10 so that the assembled battery 10 can be maintained at a temperature higher than room temperature. The temperature adjustment can be performed by a known control means including a temperature sensor and a control circuit.

  The internal configuration will be further described with reference to FIG. FIG. 2 is a diagram schematically showing a cross section taken along the line A-A ′ of FIG. 1. The inner surface of the housing 2 is covered with a heat insulating material 7 so as to keep the entire inside of the housing warm. The material of the housing | casing 2 and the heat insulating material 7 is not specifically limited, The material selected from viewpoints, such as mechanical protection of the whole assembled battery, heat insulation, can be used. For example, it is preferable that the casing 2 is made of an aluminum alloy in terms of both weight reduction and strength. Nine unit assembled batteries 1 are arranged inside, and plate heaters are arranged as heaters 3 between every three unit assembled batteries and on both side surfaces. The unit assembled battery 1 and the heater 3 are disposed so as to be in close contact with each other, and are pressed and urged in the parallel direction by the leaf spring 6 in order to ensure the close contact. The heater is exemplified by a plate heater, and is not limited to this, but in order to heat each unit assembled battery or each unit cell constituting the unit efficiently and as uniformly as possible. A plate heater having an area as large as the side surface of the unit assembled battery is preferable. Further, the arrangement is not limited to that sandwiched between unit assembled batteries as in this example, and the number is not limited to this example. From the viewpoint of heating, it is most preferable to provide a heater for each unit assembled battery. However, when the number of heaters is increased, the cost and volume of the entire assembled battery are increased. Conversely, for example, a heater can be provided only on the inner surface of the housing, which is preferable in terms of cost and volume, but a temperature difference due to the distance between each built-in battery and the heater tends to occur. This example shows an example in which the heater 3 is arranged between every three unit assembled batteries 1 in consideration of the balance.

  In this example, adjacent surfaces of the unit assembled battery 1 (for example, the surface 11a of the unit assembled battery 1 shown on the right in FIG. 2 and the surface 11b of the unit assembled battery 1 on the left side thereof) have projections such as electrodes. It consists of flat surfaces that do not have, and is in close contact with each other. Here, the close contact means a state in which the surfaces are in contact with each other without a noticeable gap in a normal sense. In other words, the surfaces are in contact with each other so that the fluid does not easily flow between the surfaces. State. The leaf spring 6 biases the unit assembled battery 1 and the heater 3 arranged so as to be in close contact with each other so that no gap is generated. If it is the same pressurization means, it will not be limited to a leaf | plate spring. By providing the pressurizing means, the degree of adhesion is further improved, and there is an effect that the adhesion does not collapse even if there is a long-term deformation such as vibration of the whole assembled battery or a heat insulating material.

  In this configuration, when a pressurizing unit such as a leaf spring is provided as described above, it is preferable that the connection terminal plates 4a and 4b connecting the unit assembled batteries have a configuration that does not inhibit pressurization. For example, a hole for penetrating the bolt 5 in the connection terminal plate is a long hole, and the unit assembled battery 1 is fixed so as to be slightly slidable in the parallel direction. At this time, as a structure capable of maintaining electrical contact with the connection terminal plate, a disc spring or a coil spring can be interposed between the bolt 5 and the connection terminal plate 4a or 4b. On the other hand, when no pressing means such as a leaf spring is provided, it is preferable that the connection terminal plates 4a and 4b are firmly tightened and fixed by the bolts 5 in a state where the unit assembled battery 1 is in close contact.

  The surface of the unit assembled battery is preferably a metal. The surface of the unit assembled battery may be the surface of the unit cell constituting the unit assembled battery as in the example described later, or may be the surface of another case that houses the unit cell set. A metal is preferably used because of its good heat conduction. Considering weight reduction of the entire battery, aluminum or an alloy thereof is preferably used for the case. It is also preferable to use a magnesium alloy for the purpose of weight reduction. Moreover, it is preferable that surface roughness Ra of the surface to which the case is closely attached is 5 μm or less. This is because the degree of adhesion increases and heat is effectively transmitted. In this example, specifically, an aluminum alloy (material A5052) was used, the surface was polished, and the surface roughness was Ra 4.8 μm. Here, the surface roughness Ra is an arithmetic average roughness (height) measured according to JIS-B0601-2001.

  Thus, it has the following effects by comprising unit assembled batteries in close contact. First, in the case where a battery is operated by heating from a room temperature state, a process is considered in which nine unit assembled batteries reach an operable temperature after energization of each heater 3 is started. Even when the heater 3 itself heats up uniformly, the unit assembled battery that is in contact with the heater and the unit assembled battery that is not in direct contact with the heater have a unit assembled battery that is in contact with the heater. The temperature goes up first. In order for the entire assembled battery to operate, it is necessary to wait for the temperature at the part farthest from the heater to reach an operable temperature. When the unit assembled batteries are not in close contact with each other, these temperature differences appear remarkably, and it takes time from the start of heater energization to the start of operation of the assembled battery. Such a time can be shortened by adopting a structure in which the unit assembled batteries are in close contact with each other. Further, even in the operating state, by maintaining good heat conduction by adhesion, the temperature difference between unit assembled batteries can be kept small, and the entire characteristics can be effectively extracted.

  FIG. 3 is a longitudinal sectional view for explaining the internal structure of the unit assembled battery 1. The unit assembled battery 1 is an assembled battery in which a plurality of unit cells are electrically connected in series to increase the battery voltage. The unit assembled battery itself is also an assembled battery of the present invention. In this example, an example in which four unit cells 20 are connected as shown in FIG. 3 is shown, but the number of connections is not limited to four. For example, if the unit cell is a molten salt battery with a voltage of 3 V, the number of connections is set to four, so that the nominal voltage as a unit assembled battery is 12 V, and it can be used as a battery corresponding to an existing lead acid battery for automobiles, etc. It is preferably used because it can be easily used for a device (for example, a charger) used for the battery. FIG. 4 is a diagram for explaining the structure of a molten salt battery as the unit cell 20 constituting FIG. 3. FIG. 4A is a top view schematically showing the internal structure of the molten salt battery, and B is the molten salt battery. It is a longitudinal cross-sectional view which shows the structure of a battery typically.

  First, the unit cell 20 will be described with reference to FIGS. In the molten salt battery of this example, a plurality (six in the figure) of negative electrodes 21 of a rectangular flat plate and a plurality (five in the figure) of positive electrodes 41 of a rectangular flat plate respectively accommodated in a bag-like separator. They are arranged in parallel in the horizontal direction (front-rear direction in the figure) so as to alternately face each other along the vertical direction. One set of negative electrode 21, separator 31 and positive electrode 41 constitute one power generation element, and in this embodiment, five power generation elements and one other negative electrode 21 are laminated to form a battery container made of a rectangular parallelepiped aluminum alloy. Is housed inside. The battery container includes a container body 25 having an opening on the upper surface, and a rectangular flat plate-like cover body 26 that is fitted in a step formed on the inner periphery of the opening of the container body 25 to close the opening. ing. The inside of the battery container is insulated by a fluororesin coating.

  The lower end portions of the connection tabs 22 made of a rectangular aluminum alloy for taking out current are joined to the upper end portions of the negative electrodes 21 on the side close to the one side wall 25A located on the short side of the container body 25, respectively. ing. The connection tab 22 and the upper part thereof are welded to two opposing surfaces of the two arm portions 231 and 231 included in the connection member 23 having a U-shape that is open to the side wall 25B in plan view. The connection member 23 has a rectangular connection plate portion 232 whose surface direction is parallel to the arm portion 231, and an attachment hole 233 that faces the through hole 25 </ b> H formed in the side wall 25 </ b> A at the upper center of the connection plate portion 232. Is provided.

  The lower end portions of the connection tabs 42 made of a rectangular aluminum alloy for taking out current are joined to the upper end portions of the positive electrodes 41 on the side close to the other side wall 25B located on the short side of the container body 25, respectively. ing. The connection tab 42 and the upper part thereof are welded to two opposing surfaces of the two arm portions 431 and 431 included in the connection member 43 having a U-shape that is open to the side wall 25A in plan view. The connection member 43 has a rectangular connection plate portion 432 whose surface direction is parallel to the arm portion 431, and an attachment hole 433 facing the through hole 25 </ b> H provided in the side wall 25 </ b> B at the upper center of the connection plate portion 432. Is provided. In this way, the above-described five power generation elements and one negative electrode 21 are electrically connected in parallel to constitute a molten salt battery having a large battery capacity.

  The negative electrode 21 is made of an aluminum foil plated with tin, which is a negative electrode active material. Aluminum is a material suitable for the current collector of each positive / negative electrode, and has corrosion resistance against molten salt. The thickness of the negative electrode 21 including the active material is about 0.14 mm, and the dimensions in the vertical direction and the horizontal direction are 100 mm and 120 mm, respectively. The size of the container body is 150 × 180 × 38 mm.

The positive electrode 41 uses an aluminum alloy porous body as a current collector, and the current collector is filled with a mixture containing a binder, a conductive auxiliary agent, and NaCrO _{2 as a} positive electrode active material, and has a thickness of about 1 mm. It is formed. The vertical dimension and the horizontal dimension of the positive electrode 41 are smaller than the vertical and horizontal dimensions of the negative electrode 21 in order to prevent the generation of dendrites. The outer edge of the positive electrode 41 is connected to the negative electrode via the separator 31. It opposes the peripheral part of 21. FIG. The current collector of the positive electrode 41 may be a non-woven fabric made of fibrous aluminum, for example.

  The separator 31 is made of a fluororesin film that is resistant to molten salt at a temperature at which the molten salt battery operates, and is formed so as to be porous and in a bag shape. The separator 31 is immersed together with the negative electrode 21 and the positive electrode 41 from a position of about 10 mm below the liquid level of the molten salt 30 filled in a rectangular parallelepiped battery container. Thereby, a slight drop in the liquid level is allowed.

  Each of the connection members 23 and 43 serves as an external electrode for connecting the negative electrode 21 and the positive electrode 41 to an external electric circuit, and is located above the liquid surface of the molten salt 30. . The molten salt 30 is composed of an FSI (bisfluorosulfonylimide) or TFSI (bistrifluoromethylsulfonylimide) anion and a cation of sodium and / or potassium, but is not limited thereto.

  In the above-described configuration, by heating the entire battery container to 85 ° C. to 95 ° C. using an external heating means, the molten salt 30 is melted, and charging and discharging through the connecting members 23 and 43 are possible. Become.

  Hereinafter, the unit assembled battery 1 will be described with reference to FIGS. 3 and 4. Four molten salt batteries as the unit cells 20 are arranged so that the side walls on the short side of the adjacent container bodies 25 are in close contact with each other. In each container body 25, the five power generating elements (the negative electrode 21, the positive electrode 41 wrapped in the separator 31) and one negative electrode 21 and the molten salt 30 connected in parallel by the connecting members 23 and 43 are incorporated. Yes. A through-hole 25H penetrating in the lateral direction is provided in the upper center of the adhered side wall, and an insulating bushing (bearing cylinder) made of Teflon (registered trademark) or the like is opened in the through-hole 25H. A bolt 51 made of an aluminum alloy is inserted. The bolt 51 is fastened by a nut 52 made of aluminum alloy, and the unit cell 20 is fixed and electrically connected in series.

  Next, the conductive material used for the molten salt battery will be described. When a metal (conductive material) having a different ionization tendency is placed at a site in contact with the electrolyte, such as the molten salt 30, electric corrosion occurs due to current flowing from one metal to the other. For this reason, in this embodiment, as described above, the connection tabs 22 and 42, the connection members 23 and 43, the bolt 51 and the nut 52 are made of the same conductive material as the negative electrode 21 and the positive electrode 41 (in this embodiment, aluminum). Alloy) and the occurrence of electrolytic corrosion is prevented. As described above, the battery container is also made of an aluminum alloy.

  As described above, the unit cells 20 are arranged so that the side surfaces of the battery containers are in close contact with each other to form the unit assembled battery 1, and the unit assembled cells 1 are in close contact with the side surfaces of the unit cells 20 as the constituent elements. Thus, the entire assembled battery 10 is arranged. Thereby, the heat generated by the heater 3 which is a heating means is efficiently transmitted to the adjacent unit assembled battery or unit cell via the respective contact surfaces. Therefore, as an effect peculiar to a battery that is operated while being held at a temperature higher than room temperature with a heating means in this way, the temperature of each incorporated unit cell is kept uniform and the temperature is raised in a short time. As a result, advantages such as shortening the operation start time can be obtained.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited thereto. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

DESCRIPTION OF SYMBOLS 1 Unit assembled battery 2 Housing | casing 3 Heater 4a, 4b Connection terminal board 5 Bolt 6 Leaf spring 7 Heat insulating material 10 Assembly battery 11a, 11b Surface 20 Unit cell 21 Negative electrode 22, 42 Connection tab 23, 43 Connection member 231,431 Arm 232, 432 Connecting plate portion 233, 433 Mounting hole 25 Container body 25A, 25B Side wall 25H Through hole 26 Lid 30 Molten salt 31 Separator 41 Positive electrode 51 Bolt 52 Nut

Claims (7)

A battery pack in which a plurality of unit cells are combined and housed in a housing and operated at a temperature higher than room temperature,
The case forming the unit cell has a flat surface facing the other unit cell adjacent thereto,
The adjacent unit cells are assembled in a state in which the flat surfaces are in close contact with each other.   The assembled battery according to claim 1, wherein the unit cell is a molten salt battery using a molten salt that melts at a temperature higher than room temperature as an electrolyte.   The assembled battery according to claim 2, wherein a material of the case is metal, and a surface roughness Ra of the surface to be adhered is 5 µm or less.   The assembled battery according to claim 1, wherein the case has a substantially rectangular parallelepiped shape, and has an electrode on a surface different from the surface to be adhered.   The assembled battery according to any one of claims 1 to 4, further comprising: a pressurizing unit that pressurizes the unit cell in a direction in which the unit cell is in close contact.   The assembled battery according to any one of claims 1 to 5, further comprising a heater for heating the unit cell in the housing. The case forming the unit cell has a substantially rectangular parallelepiped shape,
The n unit cells are connected in series, and a set of the unit cells connected in series is connected in parallel.
Cases of unit cells connected in series and / or cases of a set of unit cells connected in parallel are assembled in a state in which their adjacent surfaces are in close contact with each other,
An assembled battery comprising at least one heating means between the set of m unit cells connected in parallel.

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