Secondary battery stack warm-up device and warm-up method

Abstract

To warm up a low-temperature secondary battery with power saving in a short time.SOLUTION: A warming-up device for a secondary battery stack that includes a plurality of secondary batteries stacked therein includes: a heat medium that warms up the secondary batteries by condensation heat, the heat medium having a boiling point equal to or less than an upper limit temperature in the operating temperature range of the secondary batteries after warming up; heat medium flow passage formation parts each disposed between the plurality of secondary batteries and forming a heat medium passage where the heat medium flows; a heating part connected to the heat medium passages and boiling the heat medium by heating the heat medium in a liquid state; and a transport pump transporting the heat medium from the heat medium passages to the heating part and circulating the heat medium in the heat medium passages.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to warming up a secondary battery stack. [Background technology]

[0002] A technology for regulating the temperature of a battery is known (see, for example, Patent Document 1). In the technology described in Patent Document 1, one end of a heat pipe is connected to a battery, and the other end is connected to a heat sink containing a heat storage material. The heat storage material absorbs heat from the battery through the heat sink and is cooled by the coolant flowing through the heat sink. The coolant, whose temperature has risen, is cooled by dissipating heat to the outside by a radiator. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-204151 Summary of the Invention [Problem to be solved by the invention]

[0004] In the liquid-cooling cooling method described in Patent Document 1, which uses a liquid to transfer heat, water as a heat medium has a high fluid specific heat and high cooling capacity. However, because water has a high sensible heat, the amount of heat required to cool or heat the water is large. Air-cooling methods, which use gas as a heat medium different from liquid-cooling methods, have a low fluid specific heat and low heat transport capacity. In addition, air-cooling methods have high exhaust heat loss. Therefore, there has been a demand for technology that can change the temperature of a battery (secondary battery) in a short time while saving power.

[0005] The present invention has been made to solve at least part of the above-mentioned problems, and has an object to warm up a low-temperature secondary battery in a short time while saving power. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following forms.

[0007] (1) According to one aspect of the present invention, a warm-up device for a secondary battery stack in which a plurality of secondary batteries are stacked includes: a heat medium that warms up the secondary batteries by heat of condensation, the heat medium having a boiling point equal to or lower than an upper limit temperature in an operating temperature range of the secondary batteries after warm-up; heat medium flow path forming units that are disposed between the plurality of secondary batteries and form heat medium flow paths through which the heat medium flows; a heating unit that is connected to the heat medium flow path and heats the liquid heat medium to boil it; and a transport pump that transports the heat medium from the heat medium flow path to the heating unit and circulates the heat medium within the heat medium flow path.

[0008] According to this configuration, the secondary battery stack is warmed up before discharging or charging by the heat medium heated by the heating unit. If the secondary battery stack is left in a cold region or the like and the temperature is lower than the recommended temperature for battery operation, there is a risk that the secondary battery stack will deteriorate if it is charged or discharged. Therefore, by warming up the secondary battery stack to the recommended temperature before charging or discharging, deterioration of the secondary battery stack can be suppressed. Conventionally, secondary battery stacks have been warmed up by air-cooling or liquid-cooling using a PTC (Positive Heating Coefficient) heater, for example. PTC heaters have a temperature limiter function that increases the resistance value of the heater as the upper limit temperature is approached, so excessive temperature rise of the secondary battery stack can be suppressed. On the other hand, when the upper limit temperature is approached, the resistance of the PTC heater increases, and the PTC heater In this configuration, the amount of power input to the secondary battery stack is limited, resulting in a long warm-up time for the secondary battery stack. In contrast, this configuration warms up the secondary battery stack using the heat of condensation of a heat medium whose boiling point is below the upper limit of the operating temperature range of the secondary batteries. Therefore, as a heating unit for heating the heat medium, a heater without a temperature limiter function other than a PTC heater can be used, and a large amount of heat can be transported by a vapor heat medium. Because the heat medium transports heat as vapor to warm the secondary batteries, the amount of heat generated by the heater is used to increase the sensible heat of the secondary battery stack via the latent heat of evaporation of the heat medium. As a result, the warm-up time for the secondary battery stack can be shortened and the warm-up energy can be reduced.

[0009] (2) In the warm-up device of the above aspect, the secondary battery stack is divided into a plurality of laminated bodies along the stacking direction, and each of the laminated bodies has a plurality of the secondary batteries stacked therein, and the heat transfer medium flow paths formed between the secondary batteries within the laminated body are connected to each other to allow the heat transfer medium to circulate. Furthermore, each of the laminated bodies may be provided with a control unit that controls the warm-up of the secondary batteries and the discharging and charging of the secondary batteries after the warm-up. According to this configuration, the secondary battery stack is divided into multiple stacks, and the control unit controls discharging and charging for each stack. The secondary batteries dissipate heat during discharging and rapid charging. Therefore, in this configuration, the stack after warming up is discharged or rapid charged, and the heat generated by the discharge or rapid charging is used for the stack that has not yet been warmed up. This further reduces the warm-up energy required to warm up the entire secondary battery stack.

[0010] (3) In the warm-up device of the above aspect, the control unit may control a connection between the heat medium flow path of one of the stacks and the heat medium flow path of another of the stacks arranged adjacent to the first stack, and when warm-up of the secondary battery stack starts, the control unit may warm up the first stack by supplying the heat medium heated by the heating unit to the heat medium flow path of the first stack in a state where the heat medium flow path of the first stack and the heat medium flow path of the other stack are not connected, and after warm-up of the first stack is completed, the control unit may start discharging the first stack in a state where the heat medium flow path of the first stack and the heat medium flow path of the other stack are connected to enable the heat medium to flow between the first stack and the other stack, and may stop heating the heat medium by the heating unit and continue transporting the heat medium by the transport pump. According to this configuration, when warming up of the secondary battery stack begins, the secondary batteries of one stack are warmed up by the heated heat medium. After warming up of the secondary batteries of one stack is completed, discharge of the one stack begins, and the heat medium flows from the one stack to the other stack adjacent to the one stack. After warming up of the one stack is completed, the heat medium is not heated by the heating unit, but is heated by heat dissipation from the one stack. Therefore, the heated heat medium flowing into the other stack warms up the secondary batteries of the other stack. As a result, after warming up of the secondary batteries of the other stack is completed, discharge of the other stack and warming up of another stack adjacent to the other stack are performed in sequence. As a result, the input energy input to warm up the secondary battery stack is only the energy input for warming up the one stack. In other words, the input energy required to warm up the entire secondary battery stack can be further reduced.

[0011] (4) In the warm-up device of the above aspect, the control unit may control a connection between the heat medium flow path of one of the stacks and the heat medium flow path of another of the stacks arranged adjacent to the one of the stacks, and when warm-up of the secondary battery stack starts, the control unit may warm up the one of the stacks by supplying the heat medium heated by the heating unit to the heat medium flow path of the one of the stacks in a state where the heat medium flow path of the one of the stacks is not connected to the heat medium flow path of the other of the stacks, and after warm-up of the one of the stacks is completed, the control unit may connect the heat medium flow path of the one of the stacks to the heat medium flow path of the other of the stacks to enable the heat medium to flow between the one of the stacks and the other of the stacks, and start charging of the one of the stacks, stop heating of the heat medium by the heating unit, and continue transporting the heat medium by the transport pump. According to this configuration, when the secondary battery stack starts to warm up, the secondary batteries of one stack are The secondary batteries of one stack are warmed up by the heated heat medium. After warm-up of the secondary batteries of one stack is completed, charging of the first stack begins, and the heat medium flows from the first stack to the other stack adjacent to the first stack. After warm-up of the first stack is completed, the heat medium is not heated by the heating unit, but is heated by heat dissipation from the first stack. Therefore, the heated heat medium flowing into the other stack warms up the secondary batteries of the other stack. As a result, after warm-up of the secondary batteries of the other heat medium is completed, charging of the other stack and warm-up of another stack adjacent to the other stack are performed in sequence. As a result, the warm-up energy required to warm up the entire secondary battery stack can be further reduced.

[0012] (5) In the warm-up device of the above aspect, the heat medium has insulating properties, and the heating unit includes an insulating container that forms a space through which the heat medium passes, and a heater that is disposed within the container and has a spiral cross section extending from the central axis of the space to the outer periphery and a curved surface extending along the central axis, and is formed of a conductive material with a low heat capacity, and the heater may be made to generate heat by applying a voltage to the central axis side and the outer periphery side of the heater. With this configuration, because the heat medium is insulating, electricity can be passed directly through the heater, allowing the heat medium to be heated by utilizing the resistance heat of the heater. Because the heater has a spirally curved surface within the container, the heater forms a large heat transfer area. Therefore, even if the heat output is increased, the heat flux decreases, allowing the temperature difference between the heat medium and the heater to be reduced while maintaining the same heat transfer coefficient. As a result, with this configuration, the wall temperature of the heat transfer surface is reduced by reducing the heat capacity of the container and increasing the heat transfer area, thereby shortening the start-up time of the heating unit.

[0013] (6) The warm-up device of the above aspect may further include a vapor pressure sensor that detects the vapor pressure of the heat medium flowing from the heating unit to the heat medium flow path, and a control unit that controls the amount of heat medium transported by the transport pump so that the vapor pressure detected by the vapor pressure sensor is equal to or less than a pressure determined from the upper limit temperature of the secondary battery. With this configuration, the vapor pressure sensor detects the vapor pressure of the heat medium flowing from the heating unit to the heat medium flow path. If the same amount of heat medium continues to flow through the heat medium flow path even after the secondary battery has warmed up, the secondary battery may be overheated. In this case, the transport pump is controlled so that the vapor pressure flowing through the heat medium flow path is equal to or lower than the pressure set by the upper limit temperature of the secondary battery, thereby adjusting the flow rate of the heat medium flowing from the heating unit to the heat medium flow path. As a result, heating of the secondary battery beyond the upper limit temperature can be prevented.

[0014] The present invention can be realized in various forms, such as a secondary battery, a secondary battery stack, a warm-up device, a secondary battery system, a method for warming up a secondary battery stack and a system including these devices, a computer program for executing these devices, a server device for distributing this computer program, a non-transitory storage medium storing the computer program, etc. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic block diagram of a secondary battery system according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic cross-sectional view of a heater. [Figure 3] FIG. 2 is an explanatory diagram of a honeycomb structure of the heating element. [Figure 4] FIG. 10 is a schematic cross-sectional view of the cell stack during discharge after warm-up is complete. [Figure 5] 4 is a flowchart of a method for controlling the warm-up device. [Figure 6] FIG. 1 is an explanatory diagram of the warm-up effect of Example 1 and Comparative Examples 1 and 2. [Figure 7] FIG. 1 is an explanatory diagram of the warm-up effect of Example 1 and Comparative Examples 1 and 2. [Figure 8] FIG. 1 is an explanatory diagram of the warm-up effect of Example 1 and Comparative Examples 1 and 2. [Figure 9] FIG. 10 is an explanatory diagram of the effect of a heater. [Figure 10] FIG. 10 is an explanatory diagram of the effect of a heater. [Figure 11] FIG. 10 is an explanatory diagram of the effect of a heater. [Figure 12] FIG. 10 is an explanatory diagram of the effect of a heater. [Figure 13] FIG. 6 is a schematic cross-sectional view of a part of a secondary battery system according to a second embodiment. [Figure 14] FIG. 2 is an explanatory diagram of an inlet and an outlet. [Figure 15] FIG. 10 is a schematic cross-sectional view of a portion of the secondary battery system after warm-up of the first stack has been completed. [Figure 16] FIG. 10 is a schematic cross-sectional view of a portion of a secondary battery system in which each stack is discharging. [Figure 17] 10A and 10B are diagrams illustrating the effect of performing warm-up and discharge for each stack. [Figure 18] 10A and 10B are diagrams illustrating the effect of performing warm-up and discharge for each stack. [Figure 19] FIG. 10 is an explanatory diagram of the effect when warming up and rapid charging are performed for each stack. [Figure 20] FIG. 10 is an explanatory diagram of the effect when warming up and rapid charging are performed for each stack. DETAILED DESCRIPTION OF THE INVENTION

[0016] First Embodiment 1. Secondary battery system configuration: FIG. 1 is a schematic cross-sectional view of a secondary battery system 100 according to one embodiment of the present invention. The secondary battery system 100 of this embodiment functions as a power source for an electric motor that drives an electric vehicle. As shown in FIG. 1, the secondary battery system 100 of this embodiment includes a cell stack (secondary battery stack) 90 in which a plurality of secondary batteries 91 are stacked, and a warm-up device 80 that warms up the cell stack 90. ​​The warm-up device 80 warms up the secondary batteries 91 before discharging or charging by utilizing the condensation heat of a heat medium 10 that has a low boiling point. By utilizing the condensation heat of the heat medium 10, the warm-up time of the cell stack 90 is shortened, and the input energy required for warm-up is reduced.

[0017] FIG. 1 shows a cross-sectional view and a block diagram of a portion of a secondary battery system 100 during warm-up. Each secondary battery 91 has a substantially rectangular parallelepiped shape. In this embodiment, the multiple secondary batteries 91 are lithium-ion batteries made of the same material and with the same shape. The multiple secondary batteries 91 are stacked horizontally via a heat medium flow path 21 through which a heat medium 10 flows. The Cartesian coordinate system CS shown in FIG. 1 is composed of an X-axis parallel to the horizontal direction, a Z-axis parallel to the vertical direction, and a Y-axis perpendicular to both the X-axis and the Z-axis. The Cartesian coordinate system CS corresponds to the Cartesian coordinate system CS shown in FIG. 2 and subsequent figures.

[0018] As shown in FIG. 1 , the warm-up device 80 includes a heat medium flow path forming section 20 that forms a heat medium flow path 21 between adjacent secondary batteries 91, a heat medium 10 that flows through the heat medium flow path 21, a pump (transport pump) 30 that transports the heat medium 10, a heater (heating section) 40 that heats the heat medium 10, a vapor pressure sensor 50 that detects the vapor pressure of the heat medium 10 that flows from the heater 40 into the heat medium flow path 21, a temperature sensor 51 that detects the temperature of the secondary batteries 91, and an ECU (Engine Control Unit (control section)) 60 that controls the pump 30 using the detected pressure and the detected temperature.

[0019] The warm-up device 80 further includes a refrigerant flow path forming section 70 that forms a refrigerant flow path 71 through which the refrigerant flows, a vapor communication space 22 above the heat medium flow paths 21 that connects the heat medium flow paths 21, and a liquid communication space 23 below the heat medium flow paths 21 that connects the heat medium flow paths 21.

[0020] The heat medium channel forming section 20 is an outer wall that forms a space through which the heat medium 10 flows. As shown in Fig. 1 , the plurality of heat medium channel forming sections 20 form heat medium channels 21 that are respectively arranged between the plurality of secondary batteries 91. In this embodiment, the heat medium channels 21 are connected to each other by vapor communication spaces 22 formed above the heat medium channel forming sections 20 and the refrigerant channel forming sections 70. The heat medium channels 21 are also connected to each other by liquid communication spaces 23 formed below the heat medium channel forming sections 20 and the secondary batteries 91.

[0021] The heat medium 10 warms up the low-temperature secondary batteries 91 by heat of condensation. The heat medium 10 has a boiling point that is equal to or lower than the upper limit temperature in the operating temperature range (5°C to 45°C) of the secondary batteries 91 after warming up. The heat medium 10 in this embodiment is a fluorocarbon-based medium with a boiling point of 29°C. The liquid heat medium 10 flowing through the heat medium flow passages 21 is transported from the heat medium flow passages 21 to the heater 40 via the liquid communication space 23 by the pump 30. The pump 30 circulates the heat medium 10 within the heat medium flow passages 21. As shown in FIG. 1 , the heater 40 is a small evaporator connected to the heat medium flow passages 21 and heats the liquid heat medium 10 to boil it. The vaporized heat medium 10 boiled by the heater 40 flows into each heat medium flow passage 21 via the vapor communication space 22.

[0022] FIG. 2 is a schematic cross-sectional view of a heater 40. FIG. 2 shows a schematic cross-sectional view of the heater 40 in the XY plane. Simply put, the cross-sectional view shown in FIG. 2 is a cross-sectional view of a pipe through which the heat medium 10 to be heated flows. As shown in FIG. 2, the heater 40 includes a container 41 that forms a cylindrical space and a heater 42 disposed within the container 41. The heat medium 10 to be heated passes through the container 41. The container 41 is made of insulating ceramics. The heater 42 has a spiral cross section extending from the central axis of the cylindrical space to the outer periphery, and has a curved surface extending along the Z axis. Note that the heater 42 has a honeycomb structure with concave and convex portions formed along the center line of the curved surface, but the cross-sectional view of FIG. 2 shows this as a simplified curve without concave and convex portions.

[0023] Fig. 3 is an explanatory diagram of the honeycomb structure of the heater 42. Fig. 3 shows a schematic perspective view of a part of the heater 42. As shown in Fig. 3, the heater 42 does not simply have a curved surface, but has irregularities formed on the curved surface. Therefore, the heat transfer area for evaporating the heat medium 10 by the heater 42 is larger than in the case of a curved surface without irregularities.

[0024] The heater 42 of this embodiment is a so-called metal honeycomb made of a conductive material with a low heat capacity. As shown in Fig. 2, the heater 42 generates heat when a voltage is applied between the center side, which is one end of the heater 42, and the outer periphery side, which is the other end of the heater 42. Heat exchange occurs between the heat transfer surface formed by the honeycomb structure of the heater 42 and the liquid heat medium 10, causing the heat medium 10 to change from liquid to vapor.

[0025] As shown in FIG. 1 , the heat transfer medium flow path forming section 20 includes an outer wall 20o adjacent to the side surface of the secondary battery 91, and a porous layer 20i arranged inside the outer wall 20o. The outer wall 20o is made of a metal material. The porous layer 20i is made of aluminum with a certain porosity. Therefore, the heat transfer medium 10 in a vapor state that flows into the heat transfer medium flow path 21 provides heat to the low-temperature secondary battery 91, condensing and liquefying it. After condensation, the heat transfer medium 10 flows vertically downward within the porous layer 20i due to capillary action and gravity, and is recirculated via the liquid communication space 23 by the pump 30.

[0026] When the secondary battery 91 is discharging or charging after warm-up is complete and the heated secondary battery 91 is to be cooled, the refrigerant flows into the refrigerant flow path 71 to cool the secondary battery 91. Therefore, when the cell stack 90 is warming up, no refrigerant flows through the refrigerant flow path 71 as shown in Fig. 1. Note that there are cases where no refrigerant flows even when the secondary battery stack 90 is charging or discharging.

[0027] 4 is a schematic cross-sectional view of the cell stack 90 during discharge after warm-up is complete. When discharging the cell stack 90 of this embodiment shown in FIG. 4, the ECU 60 supplies refrigerant to the refrigerant flow path 71 without heating the heat medium 10 with the heater 40 or transporting the heat medium 10 with the pump 30. As a result, the liquid heat medium 10 stored in the liquid communication space 23 moves upward through the porous layer 20i due to capillary action. The liquid heat medium 10 absorbs heat from the secondary battery 91 and evaporates, rising as vapor within the heat medium flow path 21 and joining the refrigerant flowing through the refrigerant flow path 71. The condensed heat medium 10 moves vertically downward through the porous body layer 20i and cools the secondary battery 91 again.

[0028] 2. Warm-up device control: The ECU 60 controls the transport amount of the heat medium 10 by the pump 30 using the vapor pressure of the heat medium 10 detected by the vapor pressure sensor 50 and the temperature of the secondary battery 91 detected by the temperature sensor 51. Specifically, when the absolute value of the difference between a preset target pressure Pt and the detected vapor pressure P is less than a threshold value ε1, the ECU 60 maintains the current flow rate F of the heat medium 10 at that time. On the other hand, when the absolute value of the difference between the target pressure Pt and the vapor pressure P is equal to or greater than the threshold value ε1, the ECU 60 controls the pump 30 so that the flow rate of the heat medium 10 is obtained by adding a correction flow rate ΔF expressed by the following equation (1) to the current flow rate F.

[0029] ΔF(mol / s)=-Vt·P / T / R / Tt···(1) Vt: Total space volume (m 3 ) T: Vapor pressure sampling time (s) Tt: Boiling point of heat transfer medium (K) R: Gas constant (J / mol / K)

[0030] When the change in the vapor pressure P over time (P / T) is increasing, the amount of vapor of the heat medium 10 in the heat medium flow path 21 is increasing, and the amount of evaporation of the heat medium 10 is greater than the amount of condensation. When the amount of vapor in the heat medium flow path 21 increases, the pressure in the heat medium flow path 21 rises, and the boiling point temperature of the heat medium 10 also rises. This may cause the temperature of the secondary battery 91 to exceed the upper limit of the operating temperature range during warm-up. In response to this, in this embodiment, the ECU 60 reduces the transport rate of the pump 30 so that the vapor pressure P does not rise above a certain level above the target pressure Pt. On the other hand, when the change in the vapor pressure P over time (P / T) is decreasing, the amount of evaporation of the heat medium 10 in the heat medium flow path 21 is less than the amount of condensation. In this case, the ECU 60 increases the amount of vapor transport of the heat medium 10 to the heat medium flow path 21, thereby shortening the warm-up time.

[0031] When the detected temperature Tb of the secondary battery 91 is equal to or higher than the target temperature Tb,t of the secondary battery 91 after warming up, the ECU 60 of this embodiment stops heating of the heat medium 10 by the heater 40 and rotation of the pump 30. On the other hand, when the temperature Tb of the secondary battery 91 is lower than the target temperature Tb,t of the secondary battery 91 after warming up, the ECU 60 continues to control the correction flow rate ΔF according to the vapor pressure P.

[0032] Fig. 5 is a flowchart of a control method for warm-up device 80. In the warm-up flow shown in Fig. 5, first, ECU 60 sets a target pressure Pt and a target temperature Tb,t (step S1). Target pressure Pt and target temperature Tb,t may be set, for example, by accepting an operation by a user, or may be set by some other method.

[0033] The ECU 60 starts heating the heat medium 10 using the heater 40 and transports the heat medium 10 to the heat medium flow path 21 using the pump 30 (step S2). In this embodiment, the pump 30 transports the heat medium 10 according to a preset initial transport amount. The vapor pressure sensor 50 detects the vapor pressure P of the heat medium 10 transported from the heater 40 to the heat medium flow path 21, and the temperature sensor 51 detects the temperature Tb of the secondary battery 91 (step S3). The ECU 60 calculates the amount of change P / T in the vapor pressure P using the detected vapor pressure P and the sampling time T.

[0034] The ECU 60 determines whether the absolute value of the difference between the target pressure Pt and the steam pressure P is less than the threshold value ε1 (step S4). If it is determined that the absolute value of the difference is less than the threshold value ε1 (step S4: YES), the ECU 60 performs the process of step S7, which will be described later. If it is determined that the absolute value of the difference is equal to or greater than the threshold value ε1 (step S4: NO), the ECU 60 performs the calculation The ECU 60 calculates the correction flow rate ΔF by substituting the change P / T in the vapor pressure P into the above formula (1) (step S5). The ECU 60 sets the rotation speed of the pump 30 so that the transport rate of the heat transfer medium 10 is the sum of the current flow rate F and the correction flow rate ΔF (step S6).

[0035] The ECU 60 determines whether the temperature Tb of the secondary battery 91 detected by the temperature sensor 51 is equal to or higher than the target temperature Tb,t (step S7). If it is determined that the temperature Tb of the secondary battery is lower than the target temperature Tb,t (step S7: NO), the processing from step S3 onwards, i.e., the warm-up, is continued. If it is determined that the temperature Tb of the secondary battery 91 is equal to or higher than the target temperature Tb,t (step S7: YES), the ECU 60 stops heating of the heat medium 10 by the heater 40 and rotation of the pump 30 (step S8), and the warm-up flow ends.

[0036] 3.Effects: 6 to 8 are explanatory diagrams of the warm-up effects of Example 1 and Comparative Examples 1 and 2. Each of Figures 6 to 8 shows the warm-up effects of Example 1, which warms up using a vapor transport method of a low-boiling-point medium like the warm-up device 80 of this embodiment, Comparative Example 1, which warms up using heating with a PTC heater and air cooling, and Comparative Example 2, which warms up using heating with a PTC heater and liquid cooling.

[0037] FIG. 6 shows the change over time in the heat transport rate for one secondary battery 91. Example 1 is shown by the solid line change curve C01, Comparative Example 1 is shown by the dashed-dotted line change curve C11, and Comparative Example 2 is shown by the dashed line change curve C21. In FIGS. 6 and 7, the rate of temperature rise of the PTC heater from an initial temperature of 0°C to 29°C is 5 min (29°C temperature rise / 5 min). As shown in FIG. 6, the heat transport rate of Example 1 is much higher than that of Comparative Examples 1 and 2.

[0038] In FIG. 7 , the temperature of the secondary battery 91 is shown by a thick solid curve C02 for Example 1, a thick dashed curve C12 for Comparative Example 1, and a thick dashed curve C22 for Comparative Example 2. Also in FIG. 7 , the temperature of the heat medium 10 flowing into the heat medium flow path 21 is shown by a thin solid curve C03 for Example 1 and a thin dashed curve C13 for Comparative Examples 1 and 2. The temperatures of the heat medium 10 in Comparative Examples 1 and 2 changed in the same way, so they are collectively shown by the curve C13. As shown by the curve C02 in FIG. 7 , the warm air in Example 1 heated the secondary battery 91 to 29°C in 3 minutes. On the other hand, as shown by the curve C22, the warm air in Comparative Example 2 took 20 minutes to heat the secondary battery 91 to 29°C. In the warm-up of Comparative Example 1, as shown by the change curve C12, it took 20 minutes to heat the secondary battery 91 up to 12° C., and the warm-up could not be completed.

[0039] FIG. 8 shows the total energy input to the warm-up device 80 within 30 minutes after the start of warm-up of the secondary battery 91, and the energy utilization rate of the input energy used for warm-up. In FIG. 8, for Example 1 and Comparative Examples 1 and 2, the input energy is shown as a bar graph on the left, and the energy utilization rate is shown as a bar graph on the right. As shown in FIG. 8, in Example 1, more than 99% of the input energy of 9.1 MJ is used for warm-up. On the other hand, in Comparative Example 1, 54.7% of the input energy of 9.7 MJ is used for warm-up, but the temperature does not reach 29°C 30 minutes after the start of warm-up. In Comparative Example 2, 10.6% of the input energy of 80.0 MJ is used for warm-up. In other words, Example 1 has the lowest input energy, and nearly 100% of the input energy is used for warm-up.

[0040] 9 to 12 are explanatory diagrams of the effect of the heater 40. When the heat generator 42 shown in FIG. 2 boils the heat medium 10, the boiling state of the heat medium 10 changes depending on the heat transfer area of ​​the heat generator 42. FIG. 9 shows the heat flux q (= amount of heat / heat transfer area) that changes depending on the temperature difference ΔTsat (K) between the temperature of the heat transfer surface of the heat generator 42 and the saturation temperature of the heat medium 10. As shown in Figure 9, when the temperature difference ΔTsat is 10 to 10 2 In this state, nucleate boiling occurs, and the heat flux q increases as the temperature difference ΔTsat increases. 2 If the temperature exceeds this value, the system transitions to vapor film boiling, and the boiling of the heat medium 10 via the heat transfer surface of the heater 42 becomes unstable. If a large amount of vapor is generated from the heat medium 10, the temperature difference ΔTsat increases, and the boiling of the heat medium 10 becomes unstable. In contrast, in this embodiment, the heater 42 is arranged in a spiral shape within the container 41, thereby increasing the heat transfer area. As a result, the heat flux q decreases, and the heat medium 10 boils within the range of nucleate boiling, avoiding the state of vapor film boiling.

[0041] FIG. 10 shows the input energy required to raise the temperature of heater 40 by 200 K in each of Example 1 and Comparative Example 3. FIG. 11 shows a schematic cross-sectional view of heater 40z in Comparative Example 3. As shown in FIG. 11, heater 40z in Comparative Example 3 includes heater 42 similar to that in Example 1, metal piping 44 containing heater 42, and heater 43 wound around the outer surface of piping 44. Heater 43 is formed by wrapping a sheath including wire, insulating MgO, and a SUS coating around the outer surface of piping 44. The sheath has a diameter of φ4 and a length of 1.5 m.

[0042] As shown in Fig. 10, in order to increase the temperature of heater 40 of Example 1 by 200 K, 8.5 kJ is input to heater 42 and 1.8 kJ is input to container 41. On the other hand, in order to increase the temperature of heater 40z of Comparative Example 3 by 200 K, 8.5 kJ is input to heater 42, 9.0 kJ is input to piping 44, and 53.1 kJ is input to heater 43. In Comparative Example 3, a large amount of input energy is used, particularly to increase the temperature of heater 43. As shown in Fig. 10, the energy input to heater 40 of Example 1 is much smaller than the energy input to heater 40z of the Comparative Example.

[0043] 12 shows the heater rise time (s) from the start of heating until a predetermined temperature is reached for the heater 40 of Example 1 and the heater 40z of Comparative Example 3. As shown in FIG. 12, the heater rise time is 1.2 s for the heater 40 of Example 1 and 9.6 s for the heater 40z of Comparative Example 3. That is, the heater 40 of Example 1 rises in temperature instantaneously, and in a shorter time than the heater 40z of Comparative Example 3.

[0044] As described above, the warming device 80 of this embodiment includes the heat medium 10 flowing through the heat medium flow path 21, the pump 30 that transports the heat medium 10, and the heater 40 that heats the heat medium 10. The heat medium 10 has a boiling point below the upper limit temperature of the operating temperature range (5°C to 45°C) of the secondary battery 91 after warming up, and warms up the secondary battery 91 by heat of condensation. If the cell stack 90 is left in a cold region or the like and the temperature is lower than the recommended operating temperature of the secondary battery 91, charging or discharging the cell stack 90 may cause deterioration of the cell stack 90. ​​Therefore, in this embodiment, the cell stack 90 is warmed up to the recommended temperature before charging or discharging, thereby suppressing deterioration of the secondary battery stack. Conventionally, as in Comparative Examples 1 and 2, the cell stack 90 has been warmed up by an air-cooling or liquid-cooling method using a PTC heater. The PTC heater has a temperature limiter function that increases the resistance of the heater as it approaches the upper limit temperature, thereby suppressing excessive temperature rise of the secondary battery stack. On the other hand, when the temperature approaches the upper limit temperature, the resistance of the PTC heater increases, restricting the amount of power input to the PTC heater, which lengthens the warm-up time of the cell stack 90, as shown in FIG. 7 . In contrast, in this embodiment, the cell stack 90 is warmed up using the heat of condensation of the heat medium 10, which has a boiling point below the upper limit of the operating temperature range of the secondary battery 91. Therefore, as the heater 40 that heats the heat medium 10, it is possible to use a heater without a temperature limiter function and transport a large amount of heat using the vapor heat medium 10 as shown in FIG. 6 . Because the heat medium 10 transports heat as vapor to heat the secondary battery 91, the amount of heat generated by the heater 40 is used to increase the sensible heat of the secondary battery stack 90 via the latent heat of evaporation of the heat medium 10. As a result, the warm-up time of the cell stack 90 can be shortened and the warm-up energy can be reduced.

[0045] The heater 40 of this embodiment includes a container 41 that forms a cylindrical space and a heat generator 42 disposed within the container 41. The heat generator 42 has a spiral cross section extending from the central axis of the cylindrical space to the periphery and a curved surface extending along the Z axis. The heat generator 42 is formed of a conductive material with a low heat capacity. In this embodiment, the heat medium 10 is insulating, so electricity can be directly applied to the heat generator 42, and the heat medium 10 can be heated using the resistance heat of the heat generator 42. Because the heat generator 42 has a spiral curved surface within the container 41, the heat generator 42 forms a large heat transfer area. Therefore, even if the heat generation amount is increased, the heat flux q decreases, and the temperature difference ΔTsat between the heat medium 10 and the heat generator 42 can be reduced while maintaining the same heat transfer coefficient. As a result, the reduced heat capacity of the container 41 and the increased heat transfer area of ​​the heat generator 42 reduce the wall temperature of the heat transfer surface, thereby shortening the start-up time of the heater 40.

[0046] Furthermore, the ECU 60 of this embodiment controls the amount of heat medium 10 transported by the pump 30 using the vapor pressure of the heat medium 10 detected by the vapor pressure sensor 50. If the same amount of heat medium 10 continues to flow into the heat medium flow path 21 even after the warm-up of the secondary battery 91 has progressed, the secondary battery 91 may be overheated. In this case, the pump 30 is controlled so that the vapor pressure of the heat medium 10 flowing into the heat medium flow path 21 is equal to or lower than a pressure set based on the upper limit temperature of the secondary battery, thereby adjusting the flow rate of the heat medium 10 flowing from the heater 40 into the heat medium flow path 21. As a result, heating above the upper limit temperature of the secondary battery 91 can be suppressed.

[0047] Second Embodiment FIG. 13 is a schematic cross-sectional view of a portion of a secondary battery system 100a of a second embodiment. In the second embodiment, a cell stack 90 is divided into three stacks 90A to 90C along the stacking direction. An ECU 60a of the second embodiment controls the warm-up and discharge of the secondary battery 91 for each of the stacks 90A to 90C. When warm-up of the cell stack 90 begins, the ECU 60a starts warm-up in order, starting with the first stack 90A, and after warm-up is complete, starts discharging in order, starting with the first stack 90A. FIG. 13 shows a state in which the first stack 90A has been warmed up, and the second stack 90B and the third stack 90C have not been warmed up or discharged.

[0048] 13, the secondary battery system 100a includes a first stack 90A, a second stack 90B adjacent to the first stack 90A, a third stack 90C adjacent to the second stack 90B, a DC boost converter 92, four switches SW1 to SW4, inlets VL1in to VL3in for introducing the liquid heat medium 10 into each of the stacks 90A to 90C, outlets VL1out to VL3out for discharging the liquid heat medium 10 from each of the stacks 90A to 90C, valves Vs1 to Vs3, and an ECU 60a. The heater 40 and the pump 30 are not shown in FIG. 13.

[0049] As shown in Fig. 13, the multiple secondary batteries 91 included in each of the stacks 90A to 90C are connected in series. Four switches SW1 to SW4 open and close electrical connections between the DC boost converter 92 or each of the stacks 90A to 90C under the control of the ECU 60a. In the warm-up state of the first stack 90A shown in Fig. 1, the DC boost converter 92 is not connected to any of the stacks 90A to 90C.

[0050] The valves Vs1 to Vs3 are opened and closed under the control of the ECU 60a. The opening and closing of the valve Vs1 restricts the heat medium 10 flowing from the heater 40 into the heat medium flow path 21 of the first stack 90A. As shown in FIG. 13, the valves Vs2 and Vs3 are formed on the outlet ports VL1out to VL3out side. The valve Vs2 opens and closes the connection between the heat medium flow path 21 of the first stack 90A and the heat medium flow path of the second stack 90B. The valve Vs3 opens and closes the connection between the heat medium flow path 21 of the second stack 90B and the heat medium flow path of the third stack 90C. The opening and closing of the valve Vs1 restricts the heat medium 10 flowing from the heater 40 into the heat medium flow path 21 of the first stack 90A. In the operating state, the valve Vs1 is open and the valves Vs2 and Vs3 are closed, so the heat medium flow paths 21 of the first stack 90A and the heat medium flow paths 21 of the second stack 90B are not connected.

[0051] The inlets VL1in to VL3in and the outlets VL1out to VL3out are equipped with valves that open and close under the control of the ECU 60a, and are pipes through which the heat transfer medium 10 can pass. FIG. 14 is an explanatory diagram of the inlets VL1in to VL3in and the outlets VL1out to VL3out. FIG. 14 shows a schematic cross-sectional view of the first stack 90A in the YZ plane including the inlet VL1in and the outlet VL1out. As shown in FIG. 14, the inlet VL1in is disposed vertically above, and the outlet VL1out is disposed vertically below. Therefore, when the valve of the inlet VL1in is open, the liquid heat transfer medium 10 flows through the vapor communication space 22 and the heat transfer medium flow path 21 divided by the multiple ribs Rb, moves to the liquid communication space 23, and is transported to the heater 40 via the outlet VL1out. The inlets VL1in to VL3in and the outlets VL1out to VL3out are connected by pipes and pumps (not shown). Therefore, the heat medium 10 discharged through the outlets VL1out to VL3out passes through the inlets VL1in to VL3in via a pump (not shown) and circulates within the cell stack 90.

[0052] When warming up the cell stack 90 begins, the ECU 60a closes the valve Vs2 to disconnect the heat medium flow path 21 of the first stack 90A from the heat medium flow path 21 of the second stack 90B. The ECU 60a also opens the inlet VL1in and outlet VL1out of the first stack 90A and closes the inlet VL2in, VL3in and outlet VL2out, VL3out. In this state, the ECU 60a transports the heat medium 10 using the pump 30 and heats the heat medium 10 using the heater 40, thereby warming up the first stack 90A. As a result, when the first stack 90A is warmed up, the heat medium 10 circulates within the heat medium flow path 21 included in the area AR1 shown in FIG. 13. Note that the area AR1 is merely an image, and the heat medium 10 actually circulates within the first stack 90A.

[0053] Fig. 15 is a schematic cross-sectional view of a portion of the secondary battery system 100a after the first stack 90A has been warmed up. Fig. 15 shows a state in which, after the warm-up of the first stack 90A has been completed, the first stack 90A starts discharging and the second stack 90B starts warming up. Note that in the state shown in Fig. 15, the third stack 90C has not yet been warmed up or discharged.

[0054] When the warm-up of the first stack 90A is completed, the ECU 60a closes the valve Vs1 and opens the valve Vs2. The ECU 60a connects the heat medium flow path 21 of the first stack 90A to the heat medium flow path 21 of the second stack 90B, allowing the heat medium 10 to flow between the first stack 90A and the second stack 90B. The ECU 60a controls the opening and closing of the switches SW1 and SW2 to electrically connect the secondary battery 91 of the first stack 90A to the DC boost converter 92, thereby starting the discharge of the first stack 90A. The ECU 60a opens the outlet VL2out, which was closed, to stop the heater 40 from heating the heat medium 10 and continue transporting the heat medium 10 by the pump 30.

[0055] As a result, the temperature of the secondary batteries 91 in the first stack 90A rises due to discharge. The liquid heat transfer medium 10 that flows into the first stack 90A through the inlet VL1in evaporates by absorbing heat from the secondary batteries 91. The heat transfer medium 10 that has turned into vapor flows through the valve Vs2 from the heat transfer medium flow path 21 of the first stack 90A that is discharging to the heat transfer medium flow path 21 of the second stack 90B that is warming up. The secondary batteries 91 in the second stack 90B are warmed up by the heat transfer medium 10 that has flowed into the heat transfer medium flow path 21. The heat transfer medium 10 that has condensed by raising the temperature of the secondary batteries 91 in the second stack 90B circulates through the outlet VL2out or the outlet VL1out and flows again through the inlet VL1in into the heat transfer medium flow path 21 of the first stack 90A.

[0056] When the warm-up of the second stack 90B is completed, the ECU 60a discharges the second stack 90B in addition to the first stack 90A, in the same manner as the warm-up of the second stack 90B, and starts the warm-up of the third stack 90C. When the warm-up of the third stack 90C is completed, the ECU 60a discharges each of the stacks 90A to 90C.

[0057] Fig. 16 is a schematic cross-sectional view of a portion of the secondary battery system 100a in which the stacks 90A to 90C are discharging. Fig. 16 shows a state in which all of the stacks 90A to 90C are discharging after warm-up of the third stack 90C, which was the last to be warmed up, is completed.

[0058] When the warm-up of the third stack 90C is completed, the ECU 60a closes all of the inlets VL1in to VL3in and the outlets VL1out to VL3out and leaves the valves Vs2 and Vs3 open. The ECU 60a connects the switch SW1 to the DC boost converter 92. The ECU 60a connects the secondary battery 91 of the first stack 90A to the secondary battery 91 of the second stack 90B in series using the switch SW2, and connects the secondary battery 91 of the second stack 90B to the secondary battery 91 of the third stack 90C in series using the switch SW3. The ECU 60a connects the switch SW4 to the DC boost converter 92. As a result, the secondary battery 91 of the first stack 90A, the secondary battery 91 of the second stack 90B, and the secondary battery 91 of the third stack 90C are connected in series.

[0059] 17 and 18 are explanatory diagrams of the effects when warm-up and discharge are performed for each stack. In Fig. 17, the input energy for the warm-up control of Example 2 and the warm-up control of Comparative Example 4 is shown in a hatched bar graph. In Example 2, the cell stack 90 is divided into four stacks, and warm-up and discharge are performed sequentially as in the second embodiment. In Comparative Example 4, the cell stack 90 is not divided into stacks, and warm-up and discharge are performed collectively.

[0060] In Comparative Example 4, after the entire cell stack 90 is warmed up all at once, discharge is performed at a C-rate of 1C. In Example 2, when the warm-up of the first stack is completed and the first stack is discharging while the second stack is warming up, the C-rate of the first stack during discharge is 4C. In Example 2, the current flowing through the discharging stacks is controlled so that the discharge power of the entire cell stack 90 is the same as the discharge power in Comparative Example 4. For example, when the first and second stacks of the four stacks in Example 2 are discharging and the third stack is warming up, the combined C-rate of the first and second stacks is 2C.

[0061] As shown in Figure 17, the energy input for warm-up in Example 2 is 0.6 MJ, which is about one-fourth of the 2.2 MJ in Comparative Example 4. The dashed bar graph in Example 2 in Figure 17 represents the energy required to warm up each of the second through fourth stacks. In Example 2, the energy indicated by the dashed line is generated by utilizing heat generated by the stacks during discharge. Therefore, it is not necessary to input the energy required to warm up each of the second through fourth stacks.

[0062] FIG. 18 shows, in a bar graph, the time required for the SOC (State Of Charge) to reach 0.05 after starting warm-up and discharging in Example 2 and Comparative Example 4. As shown in FIG. 18, in Comparative Example 4, it took 5 minutes for the SOC of the cell stack 90 to reach 0.05. In Example 2, the SOC decreases from the second stack to the fourth stack are unified to 0.05, and the cell stack 90 becomes capable of discharging after warm-up of the first stack is completed. Therefore, the time required for the SOC of the first stack in Example 2 to reach 0.05 is 1.2 minutes, which is shorter than that of Comparative Example 4. When the SOC of the second stack reaches 0.0 The time it takes to reach 5 is 4.1 (= 1.2 + 2.9) minutes.

[0063] As described above, in the secondary battery system 100a of the second embodiment, the cell stack 90 is divided into three stacks 90A to 90C along the stacking direction. The ECU 60a of the second embodiment controls the warm-up and discharge of the secondary battery 91 for each of the stacks 90A to 90C. That is, in the second embodiment, the ECU 60a controls the discharge for each of the stacks 90A to 90C into which the cell stack 90 is divided. A secondary battery dissipates heat during discharge. Therefore, in the second embodiment, the heat generated by discharging the stacks 90A and 90B after warm-up can be used for the stacks 90B and 90C that have not yet been warmed up. This further reduces the warm-up energy required to warm up the entire cell stack 90, as shown in FIG. 17 .

[0064] Furthermore, the ECU 60a of the second embodiment closes the valve Vs2 when starting to warm up the cell stack 90, thereby disconnecting the heat medium flow path 21 of the first stack 90A from the heat medium flow path 21 of the second stack 90B. In this state, the ECU 60a transports the heat medium 10 using the pump 30 and heats the heat medium 10 using the heater 40 to warm up the first stack 90A. After warming up of the first stack 90A is complete, the ECU 60a connects the heat medium flow path 21 of the first stack 90A to the heat medium flow path 21 of the second stack 90B, and starts discharging the first stack 90A while allowing the heat medium 10 to flow between the first stack 90A and the second stack 90B. In this case, the ECU 60a stops heating of the heat medium 10 using the heater 40 and continues transporting the heat medium 10 using the pump 30. In the second embodiment, when warming up of the cell stack 90 starts, the secondary batteries 91 of the first stack 90A are warmed up by the heated heat medium 10. After warming up of the secondary batteries 91 of the first stack 90A is completed, discharge of the first stack 90A begins, and the heat medium 10 flows from the first stack 90A to the second stack 90B adjacent to the first stack 90A. After warming up of the first stack 90A is completed, the heat medium 10 is not heated by the heater 40, but is heated by heat dissipation from the first stack 90A. Therefore, the heated heat medium 10 flowing into the second stack 90B warms up the secondary batteries 91 of the second stack 90B. As a result, after warming up of the secondary batteries 91 of the second stack 90B is completed, the second stack 90B is discharged and the third stack 90C adjacent to the second stack 90B is warmed up in sequence. As a result, the input energy required to warm up the cell stack 90 is only the input energy required to warm up the first stack 90A, as shown in FIG. 17. In other words, the input energy required to warm up the entire cell stack 90 can be further reduced. Furthermore, by increasing the C-rate of some of the stacks that are discharging, the start of discharge of the cell stack 90 can be accelerated. Furthermore, by increasing the C-rate, the amount of heat generated by the stacks that are discharging increases, and by utilizing this heat generated to warm up other stacks, the warm-up time of the other stacks can be shortened.

[0065] Third Embodiment In the third embodiment, in the secondary battery system 100a of the second embodiment, the ECU 60a controls the warm-up and charging of the secondary battery 91 for each of the three divided stacks 90A to 90C. Specifically, the ECU 60a performs rapid charging instead of discharging as in the second embodiment. In this embodiment, charging at a C rate of 3C or higher is called rapid charging.

[0066] In the third embodiment, when starting the warm-up of the cell stack 90, the ECU 60a starts the warm-up of the first stack 90A in the same manner as in the second embodiment. After the warm-up of the first stack 90A is completed, the ECU 60a starts the warm-up of the second stack 90B in the same manner as in the second embodiment, and starts rapid charging of the first stack 90A instead of discharging the first stack 90A in the second embodiment. That is, in the third embodiment, when the warm-up of the first stack 90A is completed, the ECU 60a enables the flow of the heat medium 10 between the first stack 90A and the second stack 90B in the same manner as in the second embodiment. The ECU 60a controls the opening and closing of the switch SW1 and the switch SW2 to electrically connect the secondary battery 91 of the first stack 90A to the DC boost converter 92, The rapid charging of the first stack 90A is started. The ECU 60a opens the outlet VL2out, which was closed, to stop the heater 40 from heating the heat medium 10, and causes the pump 30 to continue transporting the heat medium 10.

[0067] In the third embodiment, a refrigerant is further circulated through the refrigerant flow path 71 of the stacked body undergoing rapid charging. Since the amount of heat generated by the secondary battery 91 during rapid charging is large, in the third embodiment, the refrigerant is used to prevent excessive heating of the secondary battery 91 during rapid charging.

[0068] 19 and 20 are explanatory diagrams of the effects when warm-up and rapid charging are performed for each stack. In Fig. 19, the input energy for the warm-up control of Example 3 and the warm-up control of Comparative Example 5 is shown in a hatched bar graph. In Example 3, the cell stack 90 is divided into four stacks, and warm-up and rapid charging are performed sequentially on each of the four stacks. In Comparative Example 5, the cell stack 90 is not divided into stacks, and warm-up and rapid charging are performed collectively.

[0069] In Comparative Example 5, the entire cell stack 90 is warmed up all at once, and then rapid charging is performed at a C-rate of 3C. In Example 3, when warming up of the first stack is completed and the first stack is rapid charging while the second stack is warming up, the C-rate of the first stack during rapid charging is 12C. In Example 3, the current flowing through the discharging stack is controlled so that the power during rapid charging of the entire cell stack 90 is the same as the power during rapid charging in Comparative Example 5. For example, when the first and second stacks of the four stacks in Example 2 are rapid charging and the third stack is warming up, the C-rate of the first and second stacks combined is 6C.

[0070] As shown in FIG. 19, the energy input for warm-up in Example 3 is 0.6 MJ, which is about one-fourth of the 2.2 MJ in Comparative Example 5. The dashed bar graph in Example 3 in FIG. 19 represents the energy required to warm up each of the second through fourth stacks. In Example 3, as in Example 2 shown in FIG. 17, the energy indicated by the dashed line is generated by utilizing heat generated by the stacks during rapid charging. Therefore, it is not necessary to input the energy required to warm up each of the second through fourth stacks.

[0071] FIG. 20 shows a bar graph of the time required for the SOC (State of Charge) to reach 0.20 after the start of warm-up and rapid charging in Example 3 and Comparative Example 5. As shown in FIG. 20, in Comparative Example 5, it took 5 minutes for the SOC of the cell stack 90 to reach 0.20 through rapid charging. In Example 3, rapid charging of the first stack becomes possible after warm-up of the first stack is completed. Therefore, the time required for the first stack to be charged to 0.20 in Example 3 is 1.2 minutes. Similarly, the time required for the second stack to be charged to 0.20 is 2.2 (= 1.2 + 1.0) minutes. The time required for the fourth stack to be charged to 0.20, which is the time required for all stacks in Example 3 to be charged to 0.20, is 4.2 (= 1.2 + 1.0 + 1.0 + 1.0) minutes, which is shorter than that of Comparative Example 5. That is, by controlling the warm-up and rapid charging of the third embodiment, the energy input for warming up the cell stack 90 can be suppressed and the charging time for the cell stack 90 can be shortened.

[0072] As described above, in the third embodiment, when the warm-up of the first stack 90A is completed, the ECU 60a enables the heat medium 10 to flow between the first stack 90A and the second stack 90B. The ECU 60a controls the opening and closing of the switches SW1 and SW2 to electrically connect the secondary battery 91 of the first stack 90A to the DC boost converter 92, and starts rapid charging of the first stack 90A. The ECU 60a stops the heater 40 from heating the heat medium 10, and continues to transport the heat medium 10 by the pump 30. That is, When warm-up of the stack 90 begins, the secondary batteries 91 of the first stack 90A are warmed up by the heated heat medium 10. After warm-up of the secondary batteries 91 of the first stack 90A is completed, rapid charging of the first stack 90A begins, and the heat medium 10 flows from the first stack 90A to the second stack 90B adjacent to the first stack 90A. After warm-up of the first stack 90A is completed, the heat medium 10 is not heated by the heater 40, but is heated by heat dissipation from the first stack 90A. Therefore, the heated heat medium 10 flowing into the second stack 90B warms up the secondary batteries 91 of the second stack 90B. As a result, after warm-up of the secondary batteries 91 of the first stack 90A is completed, rapid charging of the second stack 90B and warm-up of the third stack 90C adjacent to the second stack 90B are performed in this order. As a result, as shown in Fig. 19, it is possible to further reduce the warm-up energy required to warm up the entire cell stack 90. ​​Also, as shown in Fig. 20, in the third embodiment, by dividing the cell stack 90 into a plurality of stacks 90A-90C and performing warm-up and rapid charging, it is possible to shorten the time required to charge each of the stacks 90A-90C to a predetermined SOC compared to when the cell stack 90 is not divided into a plurality of stacks 90A-90C.

[0073] <Modifications of the above embodiment> The present invention is not limited to the above-described embodiment, and can be implemented in various forms without departing from the spirit of the present invention, including, for example, the following modifications: In the above-described embodiment, part of the configuration realized by hardware may be replaced by software, and conversely, part of the configuration realized by software may be replaced by hardware.

[0074] <Variation 1> The warming device 80 included in the secondary battery system 100 of the first and second embodiments is an example, and can be modified as long as it includes the heat medium 10 that warms up the secondary battery 91 by condensation heat, the heater 40 that heats the low-boiling-point medium, and the pump 30 that transports the heat medium 10. For example, the warming device 80 does not need to include the vapor pressure sensor 50, the temperature sensor 51, and the refrigerant flow path forming unit 70. The heat medium 10 may be reduced-pressure water whose boiling point is adjusted. The boiling point of the heat medium 10 may be other than 29°C, and is preferably between 5°C and 45°C.

[0075] Although the heat medium flow paths 21 are disposed between the stacked secondary batteries 91, they do not necessarily need to be formed between each secondary battery 91. For example, only one heat medium flow path 21 may be formed along the vertical direction, or a heat medium flow path 21 may be formed between each set of multiple secondary batteries 91. The heat medium flow path forming unit 20 is disposed adjacent to the secondary battery 91, but it is sufficient that the heat medium 10 is disposed in a state where it can exchange heat with the secondary battery 91. For example, another member may be disposed between the secondary battery 91 and the heat medium flow path forming unit 20. The heat medium flow path forming unit 20 includes the porous layer 20i, but it may also include only the outer wall 20o. In this case, the condensed heat medium 10 moves along the outer wall 20o to the liquid communication space 23. The porous layer 20i may have grooves formed on the heat transfer surface to increase the liquid permeation rate in the flow direction.

[0076] Although the heat medium passages 21 are connected by the vapor communication spaces 22 and the liquid communication spaces 23, the warm-up device 80 does not have to include the vapor communication spaces 22 and the liquid communication spaces 23. In this case, the heat medium 10 heated by the heater 40 may be transported to the heat medium passages 21 that are not connected to each other. Furthermore, the heat medium 10 discharged from each heat medium passage 21 may be transported to the heater 40.

[0077] In the heater 40 of the first embodiment, the heat medium 10 is heated by the heat generating element 42 in the container 41, but the heater 40 included in the warming device 80 can be modified. For example, the heater included in the warming device 80 may be a heater 40z shown in FIG. 11. Also, the heater 42 of the heater 40 shown in FIG. 2 has a curved surface that does not have a honeycomb structure. The heater 42 may have an uneven shape other than a honeycomb structure to increase the heat transfer area. In the container 41 of the first embodiment, the space through which the heat medium 10 passes is cylindrical, but it may be rectangular and may be deformed within the range in which the heater 42 is disposed. The central axis side of the heater 42 may be the center of gravity of the cross section formed by the container 41, or may be disposed closer to the interior of the space than the outer periphery of the heater 42.

[0078] <Variation 2> In the secondary battery systems 100a of the second and third embodiments, the cell stack 90 is divided into three or four laminated bodies, but the number of divisions of the cell stack 90 may be two, or five or more. In the second embodiment, the secondary battery 91 is not cooled by a refrigerant during discharging, but it may be cooled. For example, the ECU 60a may determine and control whether or not to cool the secondary battery 91 depending on the C rate of the secondary battery 91 during discharging.

[0079] In the second and third embodiments, the ECU 60a warms up the divided stack bodies one by one in turn and discharges or rapid charges them. However, other control may also be performed. For example, the ECU 60a may treat two stack bodies as one set and warm up and discharge them in turn in each set. Alternatively, the ECU 60a may warm up a number of stack bodies obtained by multiplying the number of stack bodies being discharged by a predetermined number (e.g., "2"). The ECU 60a can change the number of stack bodies to be controlled as long as the heat medium flow paths 21 of the stack bodies that warm up the stack bodies and that discharge or rapid charge the stack bodies are connected and the heat medium 10 can flow through them. The ECU 60a may also perform the same control as rapid charging when simply charging the cell stack 90, rather than rapid charging the cell stack 90.

[0080] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate. [Explanation of symbols]

[0081] 10...Heating medium 20...heat transfer medium flow path forming section 20i…Porous body layer 20o…exterior wall 21...heat transfer medium flow path 22...Steam communication space 23...Liquid communication space 30...Pump (transport pump) 40...Heating device (heating part) 40z…heater 41...Container 42...heater 43...Heater 44...Plumbing 50...Vapor pressure sensor 51...Temperature sensor 60, 60a...ECU (control unit) 70... Coolant flow path forming portion 71... Refrigerant flow path 80...Warm-up device 90...Cell stack (secondary battery stack) 90A...First laminate (laminate) 90B...Second laminate (laminate) 90C...Third laminate (laminate) 91…Secondary battery 92...DC boost converter 100,100a...Secondary battery system AR1…area CS...Cartesian coordinate system ΔF…Correction flow rate F…Current flow rate P...Vapor pressure Pt: Target pressure Rb...Rib SW1~SW4…スイッチ T…サンプリングtime Tb…temperature of secondary battery Tb,t…target temperature VL1in~VL3in…flow inlet VL1out~VL3out…Flow outlet Vs1,Vs2,Vs3…バルブ Change curves for C01~C03, C11~C13, C21, C22… P / T... Changes ΔTsat…temperature difference q…heat flow jet

Claims

1. A warm-up device for a secondary battery stack in which a plurality of secondary batteries are stacked, a heat medium that warms up the secondary battery by heat of condensation, the heat medium having a boiling point equal to or lower than an upper limit temperature in an operating temperature range of the secondary battery after warming up; a heat medium flow path forming portion disposed between the plurality of secondary batteries and forming a heat medium flow path through which the heat medium flows; a heating unit connected to the heat medium flow path and heating the liquid heat medium to boil it; a transport pump that transports the heat medium from the heat medium flow path to the heating unit and circulates the heat medium within the heat medium flow path; A warm-up device comprising:

2. 2. The warm-up device according to claim 1, the secondary battery stack is divided into a plurality of stacked bodies along a stacking direction, In each of the stacks, a plurality of the secondary batteries are stacked, and the heat medium flow paths formed between the secondary batteries in the stack are connected to each other, allowing the heat medium to circulate; The warm-up device further includes a control unit for each of the stacks that controls warm-up of the secondary battery and discharge and charge after warm-up.

3. 3. The warm-up device according to claim 2, The control unit Controlling connection between the heat transfer medium flow path of one of the stacks and the heat transfer medium flow path of another of the stacks arranged adjacent to the one of the stacks; at the start of warming up the secondary battery stack, the first stack is warmed up by supplying the heat medium heated by the heating unit to the heat medium flow path of the first stack in a state where the heat medium flow path of the first stack is not connected to the heat medium flow path of the second stack, a warm-up device that, after warm-up of the first stack is completed, connects the heat medium flow path of the first stack to the heat medium flow path of the other stack, allowing the heat medium to flow between the first stack and the other stack, starts the discharge of the first stack, stops heating the heat medium by the heating unit, and continues transporting the heat medium by the transport pump.

4. The warm-up device according to claim 2 or 3, The control unit Controlling connection between the heat transfer medium flow path of one of the stacks and the heat transfer medium flow path of another of the stacks arranged adjacent to the one of the stacks; at the start of warming up the secondary battery stack, the first stack is warmed up by supplying the heat medium heated by the heating unit to the heat medium flow path of the first stack in a state where the heat medium flow path of the first stack is not connected to the heat medium flow path of the second stack, a warm-up device that, after warm-up of the first stack is completed, connects the heat medium flow path of the first stack to the heat medium flow path of the other stack, allowing the heat medium to flow between the first stack and the other stack, starts charging the first stack, stops heating the heat medium by the heating unit, and continues transporting the heat medium by the transport pump.

5. A warm-up device according to any one of claims 1 to 4, The heat medium has insulating properties, The heating unit is an insulating container that forms a space through which the heat medium passes; a heater that is disposed within the container and has a spiral cross section extending from a central axis of the space to an outer periphery and a curved surface extending along the central axis, the heater being made of a conductive material with a low heat capacity; A warm-up device that applies voltage to the central axis side and the outer periphery side of the heater, thereby causing the heater to generate heat.

6. The warm-up device according to any one of claims 1 to 5, further comprising: a vapor pressure sensor for detecting the vapor pressure of the heat medium flowing from the heating unit to the heat medium flow path; a control unit that controls the amount of the heat medium transported by the transport pump so that the vapor pressure detected by the vapor pressure sensor is equal to or lower than a pressure determined based on the upper limit temperature of the secondary battery; A warm-up device comprising:

7. A method for warming up a secondary battery stack in which a plurality of secondary batteries are stacked, the method comprising: a heating step of warming up the secondary batteries by heat of condensation, the heat medium being a liquid having a boiling point equal to or lower than an upper limit temperature in the operating temperature range of the secondary batteries after warming up, the heat medium flowing through heat medium flow paths respectively disposed between the plurality of secondary batteries, by heating the liquid heat medium with a heating unit connected to the heat medium flow path to boil it; a transporting step of transporting the heat medium from the heat medium flow path to the heating unit and circulating the heat medium in the heat medium flow path; Perform the warm-up method.

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