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 a battery cell using a fluid cushion.SOLUTION: A battery system is equipped with 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 or between the battery cells and the end plates, a pressure acquisition unit, and a battery cell control unit, and 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 on the basis of the internal pressure of the fluid cushion.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] In recent years, research and development into secondary batteries that contribute to energy efficiency has been conducted to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. Battery systems using battery modules that combine multiple secondary batteries are used to drive vehicle motors such as electric vehicles and hybrid electric vehicles.

[0003] In battery systems, pressure is applied to all-solid-state battery cells in a cell stack to improve electrical characteristics such as high-rate characteristics. For example, studies have been conducted 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) using a pump based on the state of charge (SOC) of the cell stack (Patent Document 1). Also, studies have been conducted to place a fluid cushion between all-solid-state battery cells in the cell stack and adjust the pressure of the fluid cushion using a fluid pressure adjustment means that combines a pump and a valve (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-288168 [Patent Document 2] European Patent Application Publication No. 3886202 Summary of the Invention [Problem 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 stack including 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, the lithium ions are deposited on the negative electrode to form a lithium metal layer, and during discharging, the lithium ions released from the lithium metal layer are absorbed into 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) increases during charging, and decreases as the state of charge (SOC) decreases during discharging.

[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 a positive electrode tab 12. Examples of materials for the positive electrode current collector include aluminum, aluminum alloys, stainless steel, nickel, iron, and titanium. Examples of the positive electrode active material include layered active materials containing lithium, spinel-type active materials, and olivine-type active materials. Specific examples of the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and LiNi p Mn q Co r O2(p+q+r=1), LiNi p Al q Co r O2 (p+q+r=1), lithium manganese oxide (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 plates 17 have the effect of restraining the cell stack 10 in the stacking direction. The restraining force of the end plates 17 can adjust the surface pressure applied to the cell stack 10 by the fluid cushion 15. There are no particular restrictions on the material of the end plates 17, and various materials used for end plates for battery modules can be used.

[0024] The pressure acquisition unit 31 acquires the internal pressure of the fluid cushion 15. There are no particular limitations on the method for acquiring the internal pressure. For example, the internal pressure of the fluid cushion 15 can be acquired by measuring the internal pressure of each fluid cushion 15 using a pressure sensor. The internal pressure of the fluid cushion 15 can be calculated, for example, based on the following formula (1) which is based on Boyle's law. P×V / T=constant(1) In the 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 charging rate and the temperature of the battery cells 11 based on the internal pressure of the fluid cushion 15. The battery cell control unit 32 controls the charging rate of the battery cells 11 by charging or discharging the battery cells 11. The battery cell control unit 32 also operates the temperature regulator 33 to adjust the temperature inside the module case 20, thereby controlling the temperature of the battery cells 11.

[0026] Next, the operation of the battery system 100 of this embodiment will be described with reference to Fig. 2, taking as an example a case where the battery system 100 is used to drive a motor of an electric vehicle. Fig. 2 is a flow chart illustrating the operation of the battery system according to one 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 to lower the SOC: Activate the chiller to discharge the battery cells 11. The chiller is a cooling water circulation device. Activate the ECH to discharge the battery cells 11. The ECH is an electric water heater. Activate the CMU equalization circuit to adjust the SOC of each battery cell 11. The CMU (battery cell monitoring unit) is a controller that manages the charging and discharging of the battery cells 11. The CMU may be used to control charging of the battery cells 11 using regenerative energy, for example.

[0036] When the electric vehicle is running, the cell temperature can be lowered by operating the chiller to lower the temperature of the cooling water.

[0037] When the electric vehicle is charging, the following operations can be performed to lower the SOC: Activate the chiller to discharge the battery cells 11. Activate the ECH to discharge the battery cells 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 being charged, the cell temperature can be lowered by operating a chiller to lower the temperature of the cooling water.

[0039] When the electric vehicle is parked (not charging), the following operations can be performed to lower the SOC: Activate the chiller to discharge the battery cells 11. Activate the ECH to discharge the battery cells 11. Activate the equalization circuit of the CMU to adjust the SOC of each battery cell 11.

[0040] When the electric vehicle is parked (not being charged), the cell temperature can be lowered by operating the chiller to lower the temperature of the cooling water.

[0041] In step S7, it is determined whether the internal pressure of the fluid cushion 15 is equal to or lower than a specified lower limit. If the internal pressure of the fluid cushion 15 is equal to or lower than the specified lower limit (Yes), the process proceeds to step S70. If the internal pressure of the fluid cushion 15 exceeds the specified lower limit (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, which increases the contact resistance of the positive electrode layer, solid electrolyte layer, and negative electrode layer of the battery cell 11, and this may result in a deterioration in the characteristics of the battery cell 11. For this reason, a specified lower limit for the internal pressure of the fluid cushion 15 is set. The specified lower 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.

[0042] In step S70, the internal pressure of the fluid cushion 15 is adjusted to a lower limit specified value or higher by performing one or both of an operation to increase the SOC and an operation to increase the cell temperature. If the internal pressure of the fluid cushion 15 remains at or below the lower limit specified value even after the operation to increase the SOC, an operation to increase the cell temperature may be performed. Generally, when the SOC of a battery cell 11 increases during charging, the cell thickness increases and the internal pressure of the battery cell 11 increases. 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, thereby increasing the pressure applied to the battery cell 11 and causing the internal pressure of the battery cell 11 to increase.

[0043] When the electric vehicle is running, the following operations can be performed to increase the SOC: Stop the chiller Stop the ECH Charge the battery cells 11 with regenerative energy.

[0044] When an electric vehicle is running, the cell temperature can be increased by operating the ECH to raise the coolant temperature. It is preferable to control the ECH by balancing the rate of increase in cell temperature with the rate of decrease in SOC due to increased consumption of electrical energy required for the electric vehicle.

[0045] When an 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 being charged, the cell temperature can be increased by operating the ECH to raise the temperature of the cooling water.

[0047] When an electric vehicle is parked (not charging), the following operations can be performed to increase the SOC: Stop the chiller. Stop the ECH.

[0048] When the electric vehicle is parked (not being charged), the cell temperature can be increased by operating the ECH to raise the temperature of the cooling water.

[0049] Steps S6 and S60, and steps S7 and 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 repeated continuously or intermittently.

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

[0052] The battery system 100 of this embodiment configured as described above adjusts the internal pressure of the fluid cushion 15 by controlling at least one of the charging rate and temperature of the battery cell 11 based on the internal pressure of the fluid cushion 15, and therefore does not particularly require the use of a fluid supply device. Therefore, the battery system 100 of this embodiment can be made smaller by not using a fluid supply device.

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

[0054] Although the embodiment of the present invention has been described above, the present invention is not limited to this. For example, in this embodiment, the fluid cushions 15 are arranged between the battery cells 11 and between the battery cells 11 and the end plates 17, but the arrangement positions of the fluid cushions 15 are not limited to this.

[0055] 3 is a schematic diagram showing a first modified example of a battery system according to one embodiment of the present invention. In a battery system 100a of the first modified example, a fluid cushion 15 is disposed between a battery cell 11 and an end plate 17, but is not disposed between the battery cells 11 of the cell stack 10a. Other than this, the configuration is the same as that of the battery system 100 described above, and therefore the same components are designated by the same reference numerals and their description will be omitted.

[0056] According to the battery system 100a of the first modified example, a fluid cushion 15 is disposed between the battery cell 11 and the end plate 17, and furthermore, the cell thickness of each battery cell 11 in the cell stack 10a is adjustable, so that misalignment of the battery cells 11 can be reduced even if the thickness of the battery cells 11 changes due to charging and discharging, similar to the above-described battery system 100. Furthermore, because no fluid cushion 15 is disposed between the battery cells 11, the size of the cell stack 10a can be reduced.

[0057] 4 is a schematic diagram showing a second modified example of a battery system according to one embodiment of the present invention. A battery system 100b of the second modified example has a pair of two battery cells 11, with a fluid cushion 15 disposed between the pair of battery cells 11. Other than this, the configuration is the same as that of the battery system 100 described above, and therefore the same components are denoted by the same reference numerals and their description will be omitted.

[0058] According to the battery system 100b of the second modification, fluid cushions 15 are arranged between the battery cells 11 and the end plates 17 and between pairs of battery cells 11, and further, the cell thickness of each battery cell 11 in the cell stack 10b is adjustable, so that misalignment of the battery cells 11 can be reduced even if the thickness of the battery cells 11 changes due to charging and discharging, similar to the above-described battery system 100. Furthermore, because no fluid cushions 15 are arranged between the battery cells 11, the size of the cell stack 10a can be reduced.

[0059] In the battery system 100 of this embodiment, all-solid-state lithium metal secondary batteries are used as the battery cells 11, but the battery cells 11 are not limited to this. For example, they may be non-aqueous solvent lithium metal secondary batteries that use a non-aqueous solvent as the electrolyte. The battery cells 11 used in the battery system 100 of this embodiment may be any cells whose cell thickness increases with an increase in the charge rate and decreases with a decrease in the charge rate. For example, when the cell thickness of the battery cells 11 during discharge is 100, the cell thickness during charge may be in the range of 101 to 150.

[0060] In this embodiment, the battery system 100 has been described as being used to drive an electric vehicle, but the use of the battery system 100 is not limited to this. The battery system 100 of this embodiment can also be used as a power source for driving motors for vehicles other than electric vehicles, such as hybrid electric vehicles (including plug-in hybrid electric vehicles). The battery system 100 of this embodiment can also be used as a power source for mobile terminals and as a power storage system for power generation devices. [Explanation of symbols]

[0061] 1 Battery System 3. Control Unit 10 Cell stack 11 Battery Cells 15 Fluid Cushion 17 End Plate 20 Module Case 31 Pressure acquisition unit 32 Battery cell control unit 33 Temperature controller 100, 100a, 100b battery systems

Claims

1. a battery module including a cell stack formed by stacking a plurality of battery cells and a pair of end plates disposed at both ends of the cell stack in a stacking direction, with a fluid cushion disposed at least either between the battery cells or between the battery cells and the end plates; The battery cell control unit includes a pressure acquisition unit and a battery cell control unit. The battery cell has a cell thickness that increases with an increase in the charging rate and decreases with a decrease in the charging rate; the pressure acquisition unit acquires an internal pressure of the fluid cushion; The battery cell control unit controls at least one of a charging rate and a temperature of the battery cell based on the internal pressure of the fluid cushion.

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

3. 2. The battery system according to claim 1, wherein the battery cell control unit controls at least one of the charging rate and the 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.

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