Planar heat generation body and battery system

Abstract

The present invention addresses the problem of providing a planar heat generation body that has a simple structure and is capable of efficiently maintaining a to-be-heated object at a constant temperature. A planar heat generation body that solves the abovementioned problem is such that a heating promotion unit having PTC characteristics and a temperature control unit having PCT characteristics are arranged in series. The Curie temperature of the temperature control unit is lower than the Curie temperature of the heating promotion unit. The temperature control unit is disposed closer to a portion that connects to a power source than the heating promotion unit. The supply of current to the heating promotion unit is suppressed in response to temperature increases of the temperature control unit.

Description

Planar heating element and battery system

[0001] The present invention relates to a planar heating element and a battery system.

[0002] In recent years, batteries that can be repeatedly charged and discharged have been used in a wide variety of applications. Various types of batteries have been developed. Among them, lithium-ion batteries, which use lithium in the electrodes, are used not only in home appliances but also in electric vehicles and hybrid vehicles due to their high energy density, high voltage, and long life.

[0003] Batteries operate within a temperature range that is optimal for their operation. For example, the charging efficiency of lithium-ion batteries decreases in low-temperature environments. For this reason, battery systems with built-in heaters are used in vehicles and other devices that are expected to be used in cold climates (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2015-159633

[0005] It is also known that the lithium-ion battery deteriorates when it becomes excessively hot. Therefore, the battery system described in Patent Document 1 includes a temperature sensor for detecting the battery temperature, a heater for heating the battery, and a controller for stopping heating when the battery temperature becomes too high. However, such a battery system has problems such as a tendency for the device to become large and the need for complex control. Furthermore, there is a risk of excessive temperature rise if the battery temperature control mechanism (controller, etc.) fails, which necessitates the provision of a fail-safe mechanism.

[0006] An object of the present disclosure is to provide a planar heating element with a simple structure that can efficiently heat an object to be heated and maintain it at a constant temperature, and a battery system including the same.

[0007] To solve the above problems, the present disclosure provides the following sheet heating element. [1] A sheet heating element comprising a heating promotion element having PTC characteristics and a temperature control element having PTC characteristics arranged in series, wherein the Curie temperature of the temperature control element is lower than the Curie temperature of the heating promotion element, the temperature control element is arranged closer to the power source than the heating promotion element, and an increase in temperature of the temperature control element suppresses the supply of current to the heating promotion element. [2] The sheet heating element according to [1], comprising: a base material; a counter electrode composed of two or more electrodes arranged on the base material so as to straddle the heating promotion element and the temperature control element; a first PTC resistor layer arranged to cover the counter electrode of the heating promotion element; and a second PTC resistor layer arranged to cover the counter electrode of the temperature control element. [3] The sheet heating element according to [1] or [2], wherein the area of ​​the heating promotion element is larger than the area of ​​the temperature control element. [4] The sheet heating element according to [2], wherein each of the electrodes constituting the counter electrode includes a main electrode and a comb-shaped sub-electrode connected to the main electrode, and in the heating promotion section and the temperature control section, one sub-electrode and the other sub-electrode of two of the counter electrodes are alternately arranged. [5] The sheet heating element according to any of [1] to [4], which is a heater for a battery.

[0008] The present disclosure provides the following battery system: [6] A battery system including the sheet heating element according to any one of [1] to [5] above and a plurality of battery cells, wherein the heat promotion portion of the sheet heating element is disposed between the plurality of battery cells. [7] The battery system according to [6], wherein the battery cells are lithium-ion battery cells.

[0009] According to the present disclosure, there is provided a planar heating element with a simple structure that can efficiently heat an object to be heated and maintain it at a constant temperature, and a battery system including the same.

[0010] FIG. 1A is a plan view schematically illustrating the structure of a planar heating element according to one embodiment of the present disclosure, and FIG. 1B is a cross-sectional view taken along line A-A in FIG. 1A. FIG. 2A is a schematic cross-sectional view schematically illustrating the structure of a battery system according to one embodiment of the present disclosure, and FIG. 2B is a schematic cross-sectional view schematically illustrating the structure of a battery system according to another embodiment of the present disclosure. FIG. 3A is a schematic cross-sectional view schematically illustrating the structure of a battery system according to another embodiment of the present disclosure, and FIG. 3B is a schematic cross-sectional view schematically illustrating the structure of a battery system according to another embodiment of the present disclosure. FIG. 4A is a schematic cross-sectional view schematically illustrating the structure of a battery system according to another embodiment of the present disclosure, and FIG. 4B is a schematic circuit diagram of the battery system of FIG. 4A. FIG. 5A is a schematic cross-sectional view of a low-temperature cooker using the planar heating element according to the present disclosure, and FIG. 5B is a schematic view of a constant temperature device using the planar heating element according to the present disclosure.

[0011] In this specification, a numerical range indicated by "to" means a numerical range including the numerical values ​​written before and after "to".

[0012] 1. Sheet Heater An example of a sheet heating element according to an embodiment of the present disclosure will be described using the plan view of Fig. 1A and the cross-sectional view of Fig. 1B (cross-sectional view taken along line A-A in Fig. 1A ). However, Figs. 1A and 1B are schematic views of the sheet heating element 100 of this embodiment and do not show the actual dimensions or structure. Furthermore, in Figs. 1A and 1B , the first PTC resistor layer 12 and the second PTC resistor layer 22 are depicted as transparent members in order to illustrate the planar structure of the counter electrode, but these are not limited to being transparent members.

[0013] As shown in Figures 1A and 1B, the planar heating element 100 of this embodiment has a heating promotion unit 10 for increasing the temperature of an object to be heated (not shown) and a temperature control unit 20 for controlling the temperature of the object to be heated at a constant temperature, and these are arranged in series. Both the heating promotion unit 10 and the temperature control unit 20 have PTC (positive temperature coefficient) characteristics. When current is applied, the temperature rises, and when a predetermined temperature is reached, the electrical resistance increases and the temperature rise stops. On the other hand, when the temperature drops, current is applied again, and the temperature rises to the predetermined temperature.

[0014] In the planar heating element 100 of this embodiment, the Curie temperature of the temperature control unit 20 is set lower than the Curie temperature of the heating promotion unit 10. In this embodiment, the Curie temperature of the temperature control unit 20 is set near the target heating temperature of the object to be heated. For example, when the object to be heated is a lithium-ion battery, it is preferable to set the Curie temperature (target heating temperature) of the temperature control unit 20 to approximately 30°C. On the other hand, the Curie temperature of the heating promotion unit 10 is set to a temperature higher than the target heating temperature of the object to be heated but lower than the heat-resistant temperature of the object to be heated. By setting the Curie temperature of the heating promotion unit 10 higher than the target heating temperature, the temperature of the heating promotion unit 10 can be raised to a temperature higher than the target heating temperature, making it possible to heat the object to a predetermined temperature in a shorter time. On the other hand, by setting the Curie temperature of the heating promotion unit 10 lower than the heat-resistant temperature of the object to be heated, it is possible to reduce the likelihood of thermal damage to the object to be heated by the heat from the heating promotion unit 10. When the object to be heated is a lithium ion battery, the Curie temperature of the heating promotion part 10 is preferably set to more than 30°C and not more than 60°C.

[0015] Furthermore, in the sheet heating element 100 of this embodiment, the temperature control unit 20, which has a relatively low Curie temperature, is arranged closer to the power source (to the terminal 5, which is the connection portion to the power source, in this embodiment) than the heating promotion unit 10. The planar shapes of the heating promotion unit 10 and the temperature control unit 20 are selected appropriately depending on the application and usage of the sheet heating element 100, but the temperature control unit 20 is arranged so that the supply of current to the heating promotion unit 10 is suppressed when the temperature of the temperature control unit 20 rises and its electrical resistance increases. Note that the area ratio of the heating promotion unit 10 to the temperature control unit 20 is selected appropriately, but from the perspective of efficiently heating the heated object, it is preferable that the area of ​​the heating promotion unit 10 be larger than the area of ​​the temperature control unit 20. Furthermore, the heating promotion unit 10 and the temperature control unit 20 may be arranged in close contact depending on the usage of the sheet heating element 100, but it is preferable that they be arranged so that the temperature control unit 20 is not excessively affected by the heat from the heating promotion unit 10. For example, it is preferable to arrange the heating promotion unit 10 and the temperature control unit 20 with an appropriate gap therebetween.

[0016] The planar heating element 100 is typically used by placing the heating promotion unit 10 in a position where it can easily come into contact with the object to be heated, such as inside the object, and the temperature control unit 20 in a position where the temperature of the object to be heated is likely to be low, such as near the boundary between the object to be heated and the outside air. By arranging the heating promotion unit 10 and the temperature control unit 20 in this manner, when the temperature of the object to be heated is low, the heating promotion unit 10 (and the temperature control unit 20) can efficiently raise the temperature of the object to be heated. Then, when the temperature of the entire object to be heated rises and the temperature of the object near the temperature control unit 20 rises to near the heating target temperature, the electrical resistance of the temperature control unit 20 increases. This suppresses the supply of current to the heating promotion unit 10, limiting heating by the heating promotion unit 10. As a result, the temperature of the object to be heated is maintained near the heating target temperature. The planar heating element 100 has an extremely simple structure and has the advantage of not requiring a temperature sensor or a complex control device.

[0017] (Configuration of Sheet Heating Element 100) The configuration of the sheet heating element 100 of this embodiment will be described in detail. However, the sheet heating element 100 of the present invention is not limited to this configuration. The sheet heating element 100 of this embodiment has a substrate 1, counter electrodes (hereinafter also referred to as "plurality of electrodes 2, 3, 4") arranged on the substrate 1 and spanning the heating promotion section 10 and the temperature control section 20, a pair of terminals 5 for connecting the plurality of electrodes 2, 3, 4 to a power source (not shown), a first PTC resistor layer 12 arranged to cover the counter electrodes of the heating promotion section 10 (the first electrode 2 and the second electrode 3 in FIG. 1A ), and a second PTC resistor layer 22 arranged to cover the electrodes of the temperature control section 20 (the second electrode 3 and the third electrode 4 in FIG. 1A ). 1A and 1B, the sheet heating element 100 has a plurality of electrodes 2, 3, 4, terminals 5, a first PTC resistor layer 12, and a second PTC resistor layer 22 arranged on only one surface of the substrate 1. However, these may also be arranged on both surfaces of the substrate 1. The sheet heating element 100 may also have other components. Each component will be described below.

[0018] The substrate 1 is not particularly limited as long as it has insulating properties and allows for lamination of the plurality of electrodes 2, 3, 4, the first PTC resistor layer 12, and the second PTC resistor layer 22. For example, it may be composed of one layer, or two or more layers. The material of the substrate 1 is appropriately selected depending on the application of the sheet heating element 100. For example, when the sheet heating element 100 is used to heat a battery cell, it is preferable that the substrate 1 has flexibility that allows it to conform to the shape of the battery cell. On the other hand, depending on the application, the substrate 1 may have rigidity.

[0019] The material of the substrate 1 may be a resin or an inorganic material. Examples of resins include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyolefins such as polyethylene (PE), polypropylene (PP), polystyrene, ethylene vinyl acetate (EVA), cycloolefin polymer (COP), and cycloolefin copolymer (COC), vinyl resins, polycarbonate (PC), polyamide, polyimide, acrylic resin, triacetyl cellulose (TAC), polyphenylene sulfide (PPS), and the like. Examples of inorganic materials include glass and ceramic. The material of the substrate 1 of the heating promotion unit 10 and the material of the substrate 1 of the temperature control unit 20 may be the same or different. In this embodiment, the substrate 1 may be composed of multiple materials.

[0020] The planar shape and thickness of the substrate 1 are selected appropriately depending on the application of the sheet heating element 100. For example, the substrate 1 may be flat, such as a film or plate. The substrate 1 may also have any three-dimensional shape, such as a bag or box. Furthermore, as will be explained in the battery system described below, the substrate 1 may be composed of multiple films or the like that are separated from each other. The substrate 1 may or may not be translucent.

[0021] In the sheet heating element 100 of this embodiment, the counter electrode is arranged to straddle the heating promotion unit 10 and the temperature control unit 20. The counter electrode is composed of two or more electrodes. In this embodiment, it is composed of three electrodes (a first electrode 2, a second electrode 3, and a third electrode 4), and is configured so that electricity flows in series, for example, from the first electrode 2 side to the third electrode 4 side. These multiple electrodes 2, 3, and 4 are arranged so that two of them face each other and are electrically connected via the first PTC resistor layer 12 or the second PTC resistor layer 22 described below. The shape of each of the multiple electrodes 2, 3, and 4 is not particularly limited. In this embodiment, the multiple electrodes 2, 3, and 4 each include a main electrode 2a, 3a, and 4a and a comb-shaped sub-electrode 2b, 3b, and 4b electrically connected thereto, respectively.

[0022] The main electrodes 2a, 3a, and 4a and the comb-shaped sub-electrodes 2b, 3b, and 4b may be formed integrally or separately, as long as they are electrically conductive. In this embodiment, the main electrodes 2a, 3a, and 4a and the sub-electrodes 2b, 3b, and 4b are formed integrally and from the same material.

[0023] The planar shape, width, length, thickness, etc. of each of the main electrodes 2a, 3a, and 4a are appropriately selected according to the application and shape of the sheet heating element 100. In this embodiment, the main electrode 2a of the first electrode 2 and the main electrode 3a of the second electrode 3 are arranged parallel to each other. The main electrode 3a of the second electrode 3 and the main electrode 4a of the third electrode 4 are also arranged parallel to each other. Note that, in this specification, "parallel" does not only refer to perfect parallelism, but also includes cases where there is a degree of misalignment that does not impair the purpose and effects of the invention. For example, "parallel" also includes cases where the angle between two parallel lines is within 0±5°. In this embodiment, the planar shape of each of the main electrodes 2a, 3a, and 4a is linear. However, they may also be curved, zigzag, or any other shape. Their widths may be constant or may vary. Furthermore, the shapes of the two main electrodes 2 a, 3 a, 4 a in a plan view may be the same, may be symmetric (line symmetry, point symmetry, etc.), or may be asymmetric. In this embodiment, the main electrode 2 a of the first electrode 2 and the main electrode 4 a of the third electrode 4 are each provided with a terminal 5 for connection to a power source (not shown).

[0024] On the other hand, the sub-electrodes 2b, 3b, and 4b are electrodes that extend from one main electrode (e.g., main electrode 2a) to the other main electrode (here, main electrode 3a) when the sheet heating element 100 is viewed from above. In this embodiment, multiple sub-electrodes 2b, 3b, and 4b are arranged. In the heating promotion unit 10, the sub-electrodes 2b of the first electrode 2 and the sub-electrodes 3b of the second electrode 3 are arranged alternately and parallel to each other. In the temperature control unit 20, the sub-electrodes 3b of the second electrode 3 and the sub-electrodes 4b of the third electrode 4 are arranged alternately and parallel to each other. The number of sub-electrodes 2b, 3b, and 4b of the multiple electrodes 2, 3, and 4 and the spacing between them are appropriately selected depending on the size of the sheet heating element 100 and the areas of the heating promotion unit 10 and the temperature control unit 20. The length of each sub-electrode 2b, 3b, and 4b is appropriately selected depending on the areas of the heating promotion unit 10 and the temperature control unit 20. In this embodiment, the shape of each of the sub-electrodes 2b, 3b, and 4b in a plan view is linear, but the shape of the sub-electrodes 2b, 3b, and 4b may be curved, zigzag, or other shapes. However, regardless of the shape of the sub-electrodes 2b, 3b, and 4b, it is preferable that the distance between the opposing sub-electrodes is approximately constant.

[0025] The electrodes 2, 3, and 4 may be made of any material that can conduct electricity, and may be made of a metal such as aluminum or copper.

[0026] The first PTC resistor layer 12 is a layer having PTC characteristics and arranged to cover the counter electrodes (mainly the sub-electrode 2b of the first electrode 2 and the sub-electrode 3b of the second electrode 3) of the heating promotion unit 10. On the other hand, the second PTC resistor layer 22 is a layer having PTC characteristics and arranged to cover the counter electrodes (mainly the sub-electrode 3b of the second electrode 3 and the sub-electrode 4b of the third electrode 4) of the temperature control unit 20.

[0027] The first PTC resistor layer 12 and the second PTC resistor layer 22 (hereinafter collectively referred to as "PTC resistor layers 12, 22") may be made of any material, as long as they have the desired PTC characteristics. Each PTC resistor layer 12, 22 may be, for example, a layer containing a binder resin and conductive particles. In the PTC resistor layers 12, 22 containing the binder resin and the conductive particles, when a voltage is applied between the opposing electrodes (in this embodiment, the first electrode 2 and the third electrode 4), electricity flows through the layers via the conductive particles, and the temperature rises due to the electrical resistance. Meanwhile, as the temperature of the PTC resistor layers 12, 22 rises, the binder resin thermally expands, increasing the distance between the conductive particles and increasing the resistance. The electrical resistance then rises sharply near the softening temperature or melting point of the binder resin, suppressing the flow of current. That is, the PTC resistor layers 12 and 22 are controlled so that the temperature does not rise above a certain level.

[0028] Here, the rates of increase in resistance value accompanying a temperature rise of the first PTC resistor layer 12 and the second PTC resistor layer 22 may be different or the same. In particular, it is preferable that the rate of increase in resistance value accompanying a temperature rise of the second PTC resistor layer 22 be faster than the rate of increase in resistance value accompanying a temperature rise of the first PTC resistor 12. In other words, it is preferable that when the temperature of the temperature control unit 20 (second PTC resistor layer 22) reaches the desired temperature, its resistance value rises quickly and the supply of current to the heating promotion unit 10 is suppressed.

[0029] Methods for differentiating the Curie temperatures of the first PTC resistor layer 12 (heating promotion unit 10) and the second PTC resistor layer 22 (temperature control unit 20) and adjusting the rate at which the resistance value increases with increasing temperature include changing the concentration of conductive particles and the type of binder resin. While it is particularly difficult to achieve a Curie temperature of approximately 30°C with conventionally known PTC resistors, it is possible to adjust the Curie temperature of the temperature control unit 20 to approximately 30°C and increase the rate at which the resistance value increases with increasing temperature by, for example, adding wax to the second PTC resistor layer 22.

[0030] Examples of the binder resin include thermoplastic polyurethane resin, polyester resin, polyacrylate resin, polysiloxane resin, vinyl halide resin, vinylidene resin, polyimide resin, phenoxy resin, polyether resin, polyketone resin, polyvinyl butyral resin, polyvinylpyrrolidone resin, polyacrylate resin, and thermoplastic elastomer.

[0031] Examples of the conductive particles include carbon-based particles such as graphite, carbon black, multi-walled carbon nanotubes, and graphene; and metal-based particles such as nickel powder, copper powder, and silver powder.

[0032] Examples of the wax include hydrocarbon waxes such as polyethylene waxes such as low-density polyethylene wax, medium-density polyethylene wax, and high-density polyethylene wax, polypropylene wax, polybutene wax, ethylene-propylene copolymer wax, and ethylene-propylene-butene copolymer wax; vegetable waxes such as candelilla wax, carnauba wax, rice wax, Japan wax, and hydrogenated jojoba wax; animal waxes such as beeswax and lanolin wax; montan wax; ozokerite; ceresin; paraffin wax; microcrystalline wax; mineral wax; petroleum wax; higher fatty acids such as stearyl stearate and behenyl behenate; ester waxes obtained from higher fatty acids and monohydric or polyhydric lower alcohols, such as butyl stearate, propyl oleate, glyceride monostearate, glyceride distearate, and pentaerythritol tetrabehenate; ester waxes obtained from higher fatty acids and polyhydric alcohol multimers, such as diethylene glycol monostearate, dipropylene glycol distearate, diglyceryl distearate, and triglyceryl tetrastearate; sorbitan higher fatty acid ester waxes, such as sorbitan monostearate; and cholesterol higher fatty acid ester waxes, such as cholesteryl stearate.

[0033] The thickness of each PTC resistor layer 12, 22 is not particularly limited as long as it can exhibit the above-mentioned PTC characteristics. For example, a thickness of 10 μm or more is preferable, and 20 to 80 μm is more preferable. When the thickness of the PTC resistor layers 12, 22 is 10 μm or more, a sufficient amount of heat can be generated. On the other hand, when the thickness is 80 μm or less, the thickness of the sheet heating element 100 becomes thin, making it easier to apply to various uses.

[0034] The sheet heating element 100 may further include other configurations as long as the purpose and effect of this embodiment are not impaired. Examples of other configurations include, for example, attachment means for attaching the sheet heating element 100 to various devices, a protective layer, etc.

[0035] (Method for manufacturing the sheet heating element) The method for manufacturing the sheet heating element 100 is not particularly limited. First, a substrate 1 is prepared, and the above-mentioned multiple electrodes 2, 3, and 4 are formed on the substrate 1. The multiple electrodes 2, 3, and 4 can be formed by a known method. For example, aluminum foil or the like formed in a pattern may be attached to the substrate 1. Alternatively, the electrodes may be produced by cutting a metal layer formed on the substrate 1 using a blade or the like. Furthermore, the metal layer formed on the substrate 1 may be patterned using a resist. Alternatively, a desired mask may be placed on the substrate 1, and metal may be deposited by sputtering or vapor deposition. Alternatively, the multiple electrodes 2, 3, and 4 may be formed using an ink containing conductive fine particles by an inkjet method, screen printing method, a method using a dispenser, or the like.

[0036] After forming the multiple electrodes 2, 3, and 4, a first PTC resistor layer 12 is formed on the heating promotion section 10, and a second PTC resistor layer 22 is formed on the temperature control section 20. There are no particular limitations on the method for forming these, but they can be formed by dissolving or dispersing the above-mentioned binder resin, conductive particles, wax, etc. in a solvent as needed, applying it to the desired region by various application methods (roll coating, screen printing, bar coating, spin coating, inkjet printing, application with a dispenser, etc.), and then drying or solidifying it.

[0037] In the above-described embodiment, the PTC resistor layers 12 and 22 are formed on the heating promotion unit 10 and the temperature control unit 20, respectively. However, for example, a known thermistor may be disposed in the temperature control unit 20 instead of the second PTC resistor layer 22.

[0038] 2. Battery System The above-described sheet heating element can be used, for example, as a heater for a battery. Examples of battery systems using the above-described sheet heating element 100 as a battery heater will be described using Figures 2A, 2B, 3A, 3B, and 4A. However, the structure of the battery system is not limited to these.

[0039] The battery system 200 shown in FIG. 2A includes a plurality of battery cells 32 and a battery case 31 surrounding the battery cells 32. In the battery system 200, the above-described planar heating element 100 is housed inside the battery case 31, and the heating promotion units 10 of the planar heating element 100 are disposed between the plurality of battery cells 32. Meanwhile, the temperature control units 20 of the planar heating element 100 are disposed along the inner surface of the battery case 31. According to the battery system 200, the heating promotion units 10 of the planar heating element 100 can heat the battery cells 32 to a predetermined temperature in a short period of time. Meanwhile, when the temperature of the battery cells 32 reaches a heating target temperature, the resistance value of the temperature control unit 20 increases, and the supply of current to the heating promotion units 10 is suppressed. This allows the temperature of the entire battery system 200 to be maintained near the heating target temperature.

[0040] The battery system 210 shown in FIG. 2B includes a plurality of battery cells 32 and a battery case 31 surrounding the battery cells 32. In the battery system 210, the above-described planar heating element 100 is housed inside the battery case 31, and the heating promotion units 10 of the planar heating element 100 are disposed between the plurality of battery cells 32. Meanwhile, the temperature control units 20 of the planar heating element 100 are disposed along the outer periphery of the battery cells 32. According to the battery system 210, the heating promotion units 10 of the planar heating element 100 can heat the battery cells 32 to a predetermined temperature in a short period of time. Meanwhile, when the temperature of the battery cells 32 reaches the heating target temperature, the resistance value of the temperature control unit 20 increases, and the supply of current to the heating promotion units 10 is suppressed. In the battery system 210, the temperature control units 20 are disposed along the battery cells 32, enabling more accurate temperature control according to the actual temperature of the battery cells 32.

[0041] The battery system 220 shown in FIG. 3A includes a plurality of battery cells 32 and a battery case 31 surrounding the battery cells 32. In the battery system 220, the heating promotion units 10 of the planar heating element 100 are disposed between the plurality of battery cells 32, and the temperature control unit 20 is disposed along the outer periphery of the battery case 31. According to the battery system 220, the heating promotion units 10 of the planar heating element 100 can heat the battery cells 32 to a predetermined temperature in a short time. On the other hand, when the temperatures of the battery cells 32 or the battery case 31 reach a heating target temperature, the resistance value of the temperature control unit 20 increases, and the supply of current to the heating promotion unit 10 is suppressed. In the battery system 220, the temperature control unit 20 is disposed outside the battery case 31, so that the temperature can be controlled according to the temperature of the battery pack including the battery cells 32 and the battery case 31.

[0042] 3B includes a plurality of battery cells 32 and a battery case 31 that supports the battery cells 32. In the battery system 230, the heating promotion units 10 of the planar heating element 100 are disposed between the plurality of battery cells 32, and the temperature control unit 20 is disposed along the outer periphery of the battery case 31. In the battery system 230, the heating promotion units 10 of the planar heating element 100 are capable of heating the battery cells 32 to a predetermined temperature in a short time. On the other hand, when the temperatures of the battery cells 32 or the battery case 31 reach the heating target temperature, the resistance value of the temperature control unit 20 increases, and the supply of current to the heating promotion unit 10 is suppressed. In the battery system 230, because the temperature control unit 20 is disposed outside the battery case 31, it is possible to control the temperature according to the temperature of the battery pack including the battery cells 32 and the battery case 31.

[0043] The battery system 240 shown in FIG. 4A includes a plurality of battery cells 32 and a battery case 31 that supports the battery cells 32. In the battery system 240, the above-described planar heating element 100 is housed inside the battery case 31, and the heating promotion units 10 of the planar heating element 100 are disposed between the plurality of battery cells 32. Meanwhile, the temperature control units 20 of the planar heating element 100 are disposed along the outer periphery of the battery cells 32. The planar heating element 100 includes two units, each consisting of the heating promotion units 10 and the temperature control units 20, which are connected in parallel, as shown in FIG. 4B . Note that FIG. 4A does not illustrate the electrodes connecting the two units. A cooling mechanism 70 (e.g., a water-cooled tube) is disposed between the two units, and is configured to cool the battery cells 32 when their temperature rises excessively due to heat generation or the like. Note that the electrical arrangement of the two units in a battery system with a water-cooling mechanism is not limited to the configuration shown in FIG. 4B . For example, two sheet heating elements 100 may be arranged in series in the order of the (second) heat promoting portion.

[0044] In any of the battery systems having the above structures, it is possible to maintain the temperatures of the battery cells 32 and the battery case 31 near the heating target temperature. The battery system of the present invention is particularly effective for battery systems including lithium-ion battery cells.

[0045] 3. Other Applications The above-described sheet heating element can be used for purposes other than battery systems. One example of a use of a sheet heating element is a low-temperature cooker. FIG. 5A shows a cross-sectional view of the low-temperature cooker. As shown in FIG. 5A, the low-temperature cooker 300 can be configured to include a housing 41 capable of housing food therein and a sheet heating element 100 disposed on the wall and bottom surfaces of the housing 41. In the low-temperature cooker 300, the Curie temperature of the heat accelerating unit 10 can be set to approximately 100°C, and the Curie temperature of the temperature control unit 20 can be set to 60°C. In the low-temperature cooker 300, food stored in the housing 41 can be heated to a predetermined temperature in a short time using heat from the heat accelerating unit 10. On the other hand, when the temperature of the food inside reaches 60°C, the temperature control unit 20 of the sheet heating element 100 disposed on the opening side of the housing 41 suppresses the supply of current to the heat accelerating unit 10. Therefore, the temperature of the food can be maintained at approximately 60°C.

[0046] Another application of the sheet heating element is a thermostatic device (e.g., a towel steamer). Figure 5B shows a schematic diagram of a thermostatic device 400. The thermostatic device 400 can be configured to include a housing 51 for housing a desired object (e.g., a towel) and a sheet heating element 100 disposed on the wall of the housing 51. In the thermostatic device 400, the Curie temperature of the heating promotion unit 10 can be set to approximately 100°C, and the Curie temperature of the temperature control unit 20 can be set to 60°C to 80°C. This allows an object (e.g., a towel) housed in the housing 51 to be heated to a predetermined temperature in a short period of time by heat from the heating promotion unit 10. On the other hand, when the internal temperature reaches 60°C to 80°C, the temperature control unit 20 of the sheet heating element 100 suppresses the supply of current to the heating promotion unit 10. This makes it possible to maintain the internal temperature of the housing 51 at approximately 60°C to 80°C.

[0047] This application claims priority based on Japanese Patent Application No. 2024-111745, filed July 11, 2024. The contents of the specification and drawings of that application are incorporated herein by reference in their entirety.

[0048] The sheet heating element of the present disclosure can efficiently heat an object to be heated and maintain it at a constant temperature. It also has a simple structure and does not require complex control. Therefore, it is very useful as a heater for batteries and various home appliances.

[0049] REFERENCE SIGNS LIST 1 substrate 2, 3, 4 electrodes 2a, 3a, 4a main electrodes 2b, 3b, 4b auxiliary electrodes 10 heating promotion section 12 first PTC resistor layer 20 temperature control section 22 second PTC resistor layer 31 battery case 32 battery cell 41 housing 51 housing 70 cooling mechanism 100 planar heating element 200, 210, 220, 230, 240 battery system 300 low-temperature cooker 400 constant temperature device

Claims

1. A planar heating element comprising a heating promotion section having PTC characteristics and a temperature control section having PTC characteristics arranged in series, wherein the Curie temperature of the temperature control section is lower than the Curie temperature of the heating promotion section, the temperature control section is arranged closer to the power source than the heating promotion section, and a rise in temperature of the temperature control section suppresses the supply of current to the heating promotion section.

2. A planar heating element as described in claim 1, comprising: a substrate; an opposing electrode consisting of two or more electrodes arranged so as to straddle the heating promotion section and the temperature control section on the substrate; a first PTC resistor layer arranged so as to cover the opposing electrode of the heating promotion section; and a second PTC resistor layer arranged so as to cover the opposing electrode of the temperature control section.

3. The sheet heating element according to claim 1, wherein the area of ​​the heat promotion portion is larger than the area of ​​the temperature control portion.

4. The sheet heating element according to claim 2, wherein each of the electrodes constituting the opposing electrodes includes a main electrode and a comb-shaped sub-electrode connected to the main electrode, and in the heating promotion section and the temperature control section, one sub-electrode and the other sub-electrode of two of the opposing electrodes are alternately arranged.

5. The sheet heating element according to claim 1, which is a heater for a battery.

6. A battery system comprising: the sheet heating element according to any one of claims 1 to 5; and a plurality of battery cells, wherein the heat promotion portion of the sheet heating element is disposed between the plurality of battery cells.

7. The battery system according to claim 6, wherein the battery cells are lithium-ion battery cells.

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