Battery System

Abstract

To provide a battery system that does not require a particular fluid supply device, can be easily miniaturized, and can apply a predetermined pressure uniformly to battery cells using a fluid cushion. [Solution] A battery system comprising: a battery module including a cell stack in which a plurality of battery cells are stacked; and a pair of end plates arranged at both ends of the cell stack in the stacking direction, with a fluid cushion arranged at least between the battery cells and between the battery cells and the end plates; a pressure acquisition unit; and a battery cell control unit, wherein the cell thickness of the battery cells increases as the charging rate increases and decreases as the charging rate decreases, the pressure acquisition unit acquires the internal pressure of the fluid cushion, and the control unit controls at least one of the charging rate and temperature of the battery cells based on the internal pressure of the fluid cushion.

Description

Technical Field

[0001] The present invention relates to a battery system.

Background Art

[0002] In recent years, in order to enable more people to access affordable, reliable, sustainable, and advanced energy, research and development have been carried out on secondary batteries that contribute to energy efficiency. A battery system using a battery module combining a plurality of secondary batteries is used for driving vehicle motors such as electric vehicles and hybrid electric vehicles.

[0003] In a battery system, in order to improve electrical characteristics such as high-rate characteristics, pressure is applied to all-solid-state battery cells of a cell stack. For example, it has been studied to adjust the pressure applied to the cell stack using a pressure pack that expands and contracts by supplying and discharging a pressure medium (fluid) by a pump based on the state of charge (SOC) of the cell stack (Patent Document 1). Also, it has been studied to arrange a fluid cushion between all-solid-state battery cells of the cell stack and adjust the pressure of the fluid cushion by fluid pressure adjusting means combining a pump and a valve (Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the technology related to battery systems using secondary batteries, miniaturization is one of the challenges, but in conventional battery systems, a fluid supply device such as a pump is used to apply pressure to the battery cells of the cell stack using a fluid, making it difficult to miniaturize the battery system.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a battery system that does not require a fluid supply device, is easily miniaturized, and can apply a predetermined amount of pressure uniformly to battery cells using a fluid cushion, thereby contributing to improved energy efficiency. [Means for solving the problem]

[0007] The inventors discovered that the above-mentioned problems can be solved by controlling at least one of the charging rate and temperature of the battery cell based on the internal pressure of the fluid cushion, and thus completed the present invention.

[0008] (1) A battery system comprising: a battery module including a cell stack in which a plurality of battery cells are stacked; and a pair of end plates arranged at both ends of the cell stack in the stacking direction, with a fluid cushion arranged at least between the battery cells and between the battery cells and the end plates; a pressure acquisition unit; and a battery cell control unit, wherein the cell thickness of the battery cells increases as the charging rate increases and decreases as the charging rate decreases, the pressure acquisition unit acquires the internal pressure of the fluid cushion, and the battery cell control unit controls at least one of the charging rate and temperature of the battery cells based on the internal pressure of the fluid cushion.

[0009] The battery system (1) adjusts the internal pressure of the fluid cushion by controlling at least one of the charging rate and temperature of the battery cell based on the internal pressure of the fluid cushion, so there is no particular need to use a fluid supply device. Therefore, the battery system (1) can be made smaller by not using a fluid supply device.

[0010] (2) The battery system described in (1), wherein the battery cell control unit controls the battery cell so that the charging rate of the battery cell does not increase and at least one of the temperature decreases when the internal pressure of the fluid cushion is equal to or greater than a predetermined reference value of the internal pressure.

[0011] According to the battery system of (2), at least one of the charging rate and temperature of the battery cells is controlled to decrease, so that the internal pressure of the fluid cushion can be decreased without using a fluid supply device.

[0012] (3) The battery system described in (1), wherein the battery cell control unit controls at least one of the charging rate and temperature of the battery cell to increase when the internal pressure of the fluid cushion is equal to or lower than a predetermined reference value of the internal pressure.

[0013] According to the battery system of (3), at least one of the charging rate and temperature of the battery cells is controlled to increase, so that the internal pressure of the fluid cushion can be increased without using a fluid supply device. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a battery system that does not require a special fluid supply device, is easily miniaturized, and can apply a predetermined pressure uniformly to battery cells using a fluid cushion. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram illustrating the configuration of a battery system according to an embodiment of the present invention; [Figure 2] FIG. 3 is a flow chart illustrating the operation of the battery system according to the embodiment of the present invention. [Figure 3] FIG. 4 is a schematic diagram showing a first modified example of a battery system according to an embodiment of the present invention. [Figure 4] FIG. 10 is a schematic diagram showing a second modified example of a battery system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiments described below are merely examples of the present invention, and the present invention is not limited to the following.

[0017] FIG. 1 is a schematic diagram illustrating the configuration of a battery system according to one embodiment of the present invention.

[0018] As shown in FIG. 1 , a battery system 100 of this embodiment includes a battery module 1 and a control device 3. The battery module 1 includes a cell stack 10 in which a plurality of battery cells 11 are stacked, and a pair of end plates 17 arranged at both ends of the cell stack 10 in the stacking direction. Fluid cushions 15 are arranged between the battery cells 11 and between the battery cells 11 and the end plates 17. The battery module 1 is housed in a module case 20. The control device 3 adjusts the internal pressure of the fluid cushions 15 by controlling at least one of the charging rate and temperature of the battery cells 11. The control device 3 includes a pressure acquisition unit 31, a battery cell control unit 32, and a temperature regulator 33.

[0019] The battery cell 11 is an all-solid-state lithium metal secondary battery. The all-solid-state lithium metal secondary battery has an electrode laminate having a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode. The all-solid-state lithium metal secondary battery uses lithium ions as a charge transfer medium. During charging, lithium ions are deposited on the negative electrode to form a lithium metal layer. During discharging, the lithium ions released from the lithium metal layer are occluded in the positive electrode. Due to the increase and decrease in the thickness of the negative electrode caused by the formation and disappearance of the lithium metal layer, the cell thickness of the lithium metal secondary battery increases as the state of charge (SOC) during charging increases, and the cell thickness decreases as the state of charge during discharging decreases.

[0020] The positive electrode has a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material. The positive electrode current collector is connected to the positive electrode tab 12. Examples of the material of the positive electrode current collector include aluminum, aluminum alloy, stainless steel, nickel, iron, and titanium. As the positive electrode active material, for example, a layered active material containing lithium, a spinel-type active material, or an olivine-type active material can be used. Specific examples of the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), LiNi p Mn q Co r O2 (p + q + r = 1), LiNi p Al q Co r O2 (p + q + r = 1), lithium manganate (LiMn2O4), Li 1+x Mn 2-x-yExamples of the negative electrode include a hetero-element-substituted Li-Mn spinel represented by MO4 (x + y = 2, M = at least one selected from Al, Mg, Co, Fe, Ni, and Zn), lithium titanate (an oxide containing Li and Ti), and lithium metal phosphate (LiMPO4, M = at least one selected from Fe, Mn, Co, and Ni). The negative electrode has a negative electrode current collector and a metal layer that promotes uniform deposition of lithium metal. The negative electrode current collector is connected to a negative electrode tab 13. Examples of materials for the negative electrode current collector include nickel, copper, and stainless steel. Materials for the metal layer include lithium and metals that form alloys with lithium. Examples of metals that form alloys with lithium include Mg, Si, Au, Ag, In, Ge, Sn, Pb, Al, and Zn. The solid electrolyte layer includes a solid electrolyte. Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes.

[0021] The stacking direction of each layer of the battery cell 11 is the same as the stacking direction of the cell stack 10. Therefore, as the thickness of the negative electrode layer of the battery cell 11 changes, the thickness of the battery cell 11 in the stacking direction of the cell stack 10 changes. As the thickness of the battery cell 11 changes in the stacking direction, the pressure applied from the battery cell 11 to the fluid cushion 15 increases or decreases, and the internal pressure of the fluid cushion 15 changes.

[0022] The fluid cushion 15 includes an exterior body and a fluid filled inside the exterior body. The exterior body may be made of, for example, an aluminum laminate film. The fluid may be a gas or a liquid. The gas may be, for example, nitrogen. The liquid may be, for example, a mineral-based hydraulic oil, a phosphate ester-based hydraulic oil, water, or a glycol-based solvent.

[0023] The end plate 17 has the effect of restraining the cell stack 10 in the stacking direction. By the restraining force of the end plate 17, the surface pressure applied to the cell stack 10 by the fluid cushion 15 can be adjusted. The material of the end plate 17 is not particularly limited, and various materials used for the end plate of the battery module can be used.

[0024] The pressure acquisition unit 31 acquires the internal pressure of the fluid cushion 15. The method for acquiring the internal pressure is not particularly limited. As a method for acquiring the internal pressure of the fluid cushion 15, for example, a method of measuring the internal pressure of each fluid cushion 15 using a pressure sensor can be used. Further, the internal pressure of the fluid cushion 15 can be calculated based on, for example, the following formula (1) based on Boyle's law. P×V / T = constant (1) However, in formula (1), P represents the pressure of the fluid cushion, V represents the volume of the fluid cushion, and T represents the temperature of the fluid cushion.

[0025] The battery cell control unit 32 controls at least one of the charge rate and temperature of the battery cell 11 based on the internal pressure of the fluid cushion 15. The battery cell control unit 32 controls the charge rate of the battery cell 11 by charging or discharging the battery cell 11. Further, the battery cell control unit 32 controls the temperature of the battery cell 11 by operating the temperature regulator 33 to adjust the temperature inside the module case 20.

[0026] Next, the operation of the battery system 100 of the present embodiment will be described with reference to FIG. 2 by taking the case where the battery system 100 is used for driving a motor of an electric vehicle as an example. FIG. 2 is a flowchart for explaining the operation of the battery system according to an embodiment of the present invention.

[0027] First, as shown in FIG. 2, in step S1, the temperature, charging rate, and deterioration degree of the battery cell 11 are measured. The temperature of the battery cell 11 can be measured using, for example, a thermometer. The charging rate of the battery cell 11 can be obtained by measuring the potential of the battery cell 11 and substituting the obtained battery into a previously prepared relational expression between the deterioration degree, potential, and charging rate. The deterioration degree of the battery cell 11 is the degree of decrease in the charge / discharge capacity of the battery cell 11. The deterioration degree can be obtained by measuring the charge / discharge capacity of each battery cell 11 in each charge / discharge cycle. The deterioration degree can also be obtained from the increase in internal resistance of each battery cell 11 due to each charge / discharge cycle.

[0028] Next, in step S2, the thickness of each battery cell 11 is calculated. The thickness of the battery cell 11 can be calculated, for example, by substituting the data obtained in step S1 into a relational expression between the thickness of the battery cell 11, the temperature, the charging rate, and the degree of deterioration of the battery cell 11, which has been prepared in advance.

[0029] Next, in step S3, the total thickness of the fluid cushion 15 is calculated. The total thickness of the fluid cushion 15 can be calculated, for example, by subtracting the total thickness of each battery cell 11 from the total thickness of the cell stack 10.

[0030] Next, in step S4, the thickness of each fluid cushion 15 is calculated. The thickness of each fluid cushion 15 can be calculated, for example, by dividing the total thickness of the fluid cushions 15 obtained in step S3 by the number of fluid cushions 15 in the cell stack 10.

[0031] Next, in step S5, the internal pressure of each fluid cushion 15 is calculated. The internal pressure of each fluid cushion 15 can be calculated, for example, by substituting the volume V of the fluid cushion 15 obtained from the thickness of the fluid cushion 15 obtained in step S4 and the temperature T of the fluid cushion 15 measured by a thermometer into the above formula (1).

[0032] Through steps S1 to S5, the internal pressure of each fluid cushion 15 is obtained. Steps S1 to S5 are performed by the pressure acquisition unit 31.

[0033] Next, in step S6, it is determined whether the internal pressure of the fluid cushion 15 obtained in step S5 is equal to or greater than a specified upper limit. If the internal pressure of the fluid cushion 15 is equal to or greater than the specified upper limit (Yes), the process proceeds to step S60. If the internal pressure of the fluid cushion 15 is less than the specified upper limit (No), the process proceeds to step S7. If the internal pressure of the fluid cushion 15 becomes excessively high, the pressure applied from the fluid cushion 15 to the battery cells 11 and end plates 17 may become too high. For this reason, a specified upper limit for the internal pressure of the fluid cushion 15 is set. The specified upper limit for the internal pressure of the fluid cushion 15 may be set taking into account the state of the electric vehicle (e.g., while driving, charging, parked) and the charging rate of each battery cell 11.

[0034] In step S60, the internal pressure of the fluid cushion 15 is adjusted to be equal to or lower than an upper limit specified value by performing one or both of an operation to lower the SOC and an operation to lower the cell temperature. The SOC is a value that represents the state of charge (charging rate) of the battery cell 11. If the internal pressure of the fluid cushion 15 remains equal to or higher than the upper limit specified value even after the operation to lower the SOC, an operation to lower the cell temperature may be performed. Generally, when the SOC of a battery cell 11 decreases due to discharge, the cell thickness decreases, and the internal pressure of the battery cell 11 decreases. Furthermore, when the cell temperature of the battery cell 11 decreases, the temperature of the fluid cushion 15 decreases, and the internal pressure of the fluid cushion 15 decreases, thereby reducing the pressure applied to the battery cell 11 and causing the internal pressure of the battery cell 11 to decrease.

[0035] When the electric vehicle is running, the following operations can be performed as an operation to lower the SOC. Activate the chiller to discharge the battery cell 11. The chiller is a cooling water circulation device. Activate the ECH to discharge the battery cell 11. The ECH is an electric water heater. Activate the equalization circuit of the CMU to adjust the SOC of each battery cell 11. The CMU (Battery Cell Monitor Unit) is a controller that manages the charging and discharging of the battery cell 11. The CMU may be used to control the charging of the battery cell 11 by, for example, regenerative energy.

[0036] When the electric vehicle is running, as an operation to lower the cell temperature, an operation of activating the chiller to lower the water temperature of the cooling water can be performed.

[0037] When the electric vehicle is charging, the following operations can be performed as an operation to lower the SOC. Activate the chiller to discharge the battery cell 11. Activate the ECH to discharge the battery cell 11. Activate the equalization circuit of the CMU to adjust the SOC of each battery cell 11. Adjust the charging current value.

[0038] When the electric vehicle is charging, as an operation to lower the cell temperature, an operation of activating the chiller to lower the water temperature of the cooling water can be performed.

[0039] When the electric vehicle is parked (without charging), the following operations can be performed as an operation to lower the SOC. Activate the chiller to discharge the battery cell 11. Activate the ECH to discharge the battery cell 11. Activate the equalization circuit of the CMU to adjust the SOC of each battery cell 11.

[0040] When the electric vehicle is parked (without charging), as an operation to lower the cell temperature, an operation of activating the chiller to lower the water temperature of the cooling water can be performed.

[0041] In step S7, it is determined whether or not the internal pressure of the fluid cushion 15 is equal to or lower than the lower limit specified value. If the internal pressure of the fluid cushion 15 is equal to or lower than the lower limit specified value (Yes), the process proceeds to step S70. If the internal pressure of the fluid cushion 15 exceeds the lower limit specified value (No), the process proceeds to step S1. If the internal pressure of the fluid cushion 15 drops excessively, the pressure applied from the fluid cushion 15 to the battery cell 11 becomes too low, and the contact resistance of the positive electrode layer, solid electrolyte layer, and negative electrode layer of the battery cell 11 increases, which may deteriorate the characteristics of the battery cell 11. For this reason, the lower limit specified value of the internal pressure of the fluid cushion 15 is set. The lower limit specified value of the internal pressure of the fluid cushion 15 may be set in consideration of the state of the electric vehicle (for example, during driving, charging, or parking) and the charging rate of each battery cell 11.

[0042] In step S70, the internal pressure of the fluid cushion 15 is adjusted to be equal to or higher than the lower limit specified value by performing one or both of an operation to increase the SOC and an operation to increase the cell temperature. If the state where the internal pressure of the fluid cushion 15 remains equal to or lower than the lower limit specified value even when the operation to increase the SOC is performed, the operation to increase the cell temperature may be performed. Generally, when the battery cell 11 is charged and the SOC increases, the cell thickness increases when charged, and the internal pressure of the battery cell 11 increases. Also, generally, when the cell temperature of the battery cell 11 increases, the temperature of the fluid cushion 15 increases, and the internal pressure of the fluid cushion 15 increases, so that the pressure applied to the battery cell 11 increases and the internal pressure of the battery cell 11 increases.

[0043] When the electric vehicle is in motion, the following operations can be performed as an operation to increase the SOC. Stop the chiller. Stop the ECH. Charge the battery cell 11 with regenerative energy.

[0044] When the electric vehicle is in motion, as an operation to increase the cell temperature, an operation can be performed to activate the ECH and increase the water temperature of the cooling water. The ECH is preferably controlled in balance with the degree of increase in the cell temperature and the degree of decrease in the SOC due to an increase in the consumption of electrical energy required for the electric vehicle.

[0045] When the electric vehicle is charging, the following operations can be performed to increase the SOC. Stop the chiller. Stop the ECH. Increase the charging current value.

[0046] When the electric vehicle is charging, as an operation to increase the cell temperature, the operation of activating the ECH to raise the water temperature of the cooling water can be performed.

[0047] When the electric vehicle is parked (without charging), the following operations can be performed to increase the SOC. Stop the chiller. Stop the ECH.

[0048] When the electric vehicle is parked (without charging), as an operation to increase the cell temperature, the operation of activating the ECH to raise the water temperature of the cooling water can be performed.

[0049] Step S6 and step S60, step S7 and step S70 are performed by the battery cell control unit 32 and the temperature regulator 33.

[0050] The operations from step S1 to step S7 may be continuously repeated or intermittently repeated.

[0051] The upper limit specified value and the lower limit specified value of the internal pressure of the fluid cushion 15 may be set according to the state such as during the running of the electric vehicle or the charging state. Further, the upper limit specified value and the lower limit specified value of the internal pressure of the fluid cushion 15 may be set according to the charging rate of each battery cell 11.

[0052] The battery system 100 of the present embodiment configured as described above controls at least one of the charging rate and the temperature of the battery cell 11 based on the internal pressure of the fluid cushion 15, thereby adjusting the internal pressure of the fluid cushion 15. Therefore, it is not particularly necessary to use a fluid supply device. Thus, according to the battery system 100 of the present embodiment, miniaturization can be achieved by not using a fluid supply device.

[0053] According to the battery system 100 of the present embodiment, when the internal pressure of the fluid cushion 15 is equal to or higher than a preset reference value (upper limit specified value), at least one of the charging rate and temperature of the battery cell 11 is controlled to decrease. Therefore, the internal pressure of the fluid cushion 15 can be decreased without using a fluid supply device. Further, according to the battery system 100 of the present embodiment, when the internal pressure of the fluid cushion 15 is equal to or lower than a preset reference value (lower limit specified value), at least one of the charging rate and temperature of the battery cell 11 is controlled to increase. Therefore, the internal pressure of the fluid cushion can be increased without using a fluid supply device.

[0054] As described above, the embodiments of the present invention have been described, but the present invention is not limited thereto. For example, in the present embodiment, the fluid cushion 15 is disposed between the battery cells 11 and between the battery cell 11 and the end plate 17, but the arrangement position of the fluid cushion 15 is not limited thereto.

[0055] FIG. 3 is a schematic diagram showing a first modification of the battery system according to an embodiment of the present invention. In the battery system 100a of the first modification, the fluid cushion 15 is disposed between the battery cell 11 and the end plate 17 and is not disposed between the battery cells 11 of the cell stack 10a. Other than this, since it has the same configuration as the above-described battery system 100, the same reference numerals are given to the same components and the description thereof is omitted.

[0056] According to the battery system 100a of the first modification, the fluid cushion 15 is disposed between the battery cell 11 and the end plate 17, and the cell thickness can be adjusted for each battery cell 11 of the cell stack 10a. Therefore, even if the thickness of the battery cell 11 changes due to charge and discharge as in the above-described battery system 100, the displacement of the battery cell 11 can be reduced. Further, since the fluid cushion 15 is not disposed between the battery cells 11, the size of the cell stack 10a can be reduced.

[0057] FIG. 4 is a schematic diagram showing a second modification of the battery system according to an embodiment of the present invention. In the battery system 100b of the second modification, two battery cells 11 are taken as a set, and a fluid cushion 15 is disposed between the set of battery cells 11. Since the rest of the configuration is the same as that of the above-described battery system 100, the same reference numerals are given to the same components, and the description thereof is omitted.

[0058] According to the battery system 100b of the second modification, the fluid cushion 15 is disposed between the battery cell 11 and the end plate 17 and between the set of battery cells 11, and the cell thickness can be adjusted for each battery cell 11 of the cell stack 10b. Therefore, even if the thickness of the battery cell 11 changes due to charge and discharge as in the above-described battery system 100, the displacement of the battery cell 11 can be reduced. Further, since the fluid cushion 15 is not disposed between the battery cells 11, the size of the cell stack 10a can be reduced.

[0059] In the battery system 100 of the present embodiment, all-solid-state lithium metal secondary batteries are used as the battery cells 11, but the battery cells 11 are not limited thereto. For example, a non-aqueous solvent lithium metal secondary battery using a non-aqueous solvent as an electrolyte may be used. The battery cell 11 used in the battery system 100 of the present embodiment may be one in which the cell thickness increases as the charge rate increases and the cell thickness decreases as the charge rate decreases. For example, when the cell thickness during discharge is 100, the cell thickness during charging may be in the range of 101 or more and 150 or less.

[0060] In the present embodiment, the battery system 100 has been described as being used for driving an electric vehicle, but the application of the battery system 100 is not limited thereto. The battery system 100 of the present embodiment can also be used as a power source for driving a motor for vehicles other than electric vehicles, such as hybrid electric vehicles (including plug-in hybrid electric vehicles). The battery system 100 of the present embodiment can also be used as a power source for a mobile terminal and a power storage system for a power generation device.

Description of Symbols

[0061] 1 Battery system 3 Control unit 10 Cell stack 11 Battery cell 15 Fluid cushion 17 End plate 20 Module case 31 Pressure acquisition unit 32 Battery cell control unit 33 Temperature regulator 100, 100a, 100b Battery systems

Claims

1. A battery module including a cell stack in which a plurality of battery cells are stacked, and a pair of end plates disposed at both ends in the stacking direction of the cell stack, wherein a fluid cushion is disposed at least between the battery cells and between the battery cells and the end plates, a pressure acquisition unit, and a battery cell control unit, wherein the battery cell increases in cell thickness as the state of charge increases and decreases in cell thickness as the state of charge decreases, the pressure acquisition unit acquires the internal pressure of the fluid cushion, and the battery cell control unit controls at least one of the state of charge and temperature of the battery cell based on the internal pressure of the fluid cushion. A battery system.

2. The battery system according to claim 1, wherein when the internal pressure of the fluid cushion is equal to or higher than a preset reference value of the internal pressure, the battery cell control unit controls so that at least one of the state of charge of the battery cell does not increase and the temperature decreases.

3. The battery system according to claim 1, wherein when the internal pressure of the fluid cushion is equal to or lower than a preset reference value of the internal pressure, the battery cell control unit controls so that at least one of the state of charge and temperature of the battery cell increases.

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