Battery system

Abstract

To provide a battery system which includes a battery cell with a cell thickness, which increases as a charging rate rises and decreases as the charging rate lowers, and yet makes a tab of the battery cell and the battery cell itself less likely to bend when the battery cell is connected to a bus bar.SOLUTION: A battery system includes: a cell laminate in which a plurality of battery cells are laminated; a battery module which includes a pair of end plates disposed at both ends in a lamination direction of the cell laminate and in which a cushion is disposed in at least one of a space between the battery cell and the battery cell and a space between the battery cell and the end plate; and a cell thickness controller which controls cell thicknesses of the battery cells in each cell laminate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, research and development has been conducted on secondary batteries that contribute to energy efficiency in order 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. For battery systems, studies have been conducted to reduce the cell thickness of battery cells by discharging abnormal battery cells, thereby increasing the distance between the abnormal battery cells and other battery cells (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] German Patent Application Publication No. 102021105782A1 Summary of the Invention [Problem to be solved by the invention]

[0004] Increasing capacity is one of the challenges facing secondary battery technology. Lithium metal secondary batteries are known as high-capacity secondary batteries. Lithium metal secondary batteries use 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 absorbed into the positive electrode. In lithium metal secondary batteries, the cell thickness increases as the charge rate increases during charging and decreases as the charge rate decreases during discharging. In battery modules incorporating high-capacity lithium metal secondary batteries, bus bars capable of carrying large currents are widely used as conductors for connecting the battery cells. Typically, the tabs of the battery cells are connected to the bus bars by welding, for example. However, bus bars have low flexibility. Therefore, if the positions of the battery cells within the cell stack change significantly due to changes in the cell thickness caused by charging and discharging, the tabs connecting to the bus bars may bend, which may in turn bend the battery cells themselves, resulting in battery cell degradation or short-circuiting.

[0005] The present invention has been made in view of the above circumstances, and has an object to provide a battery system that uses battery cells whose cell thickness increases as the charging rate increases and decreases as the charging rate decreases, and in which the tabs of the battery cells are less likely to bend when connected to bus bars, and in which the battery cells themselves are less likely to bend. [Means for solving the problem]

[0006] The inventors discovered that the above-mentioned problems can be solved by placing a cushion in the cell stack of a battery module and further providing a cell thickness controller that enables adjustment of the cell thickness of each battery cell in the cell stack, and thus completed the present invention.

[0007] (1) A battery system comprising: a cell stack formed by stacking a plurality of battery cells; and a pair of end plates arranged at both ends of the cell stack in the stacking direction, with cushions arranged at least between the battery cells and between the battery cells and the end plates; and a cell thickness controller that controls the cell thickness of each of the battery cells in the cell stack, wherein the cell thickness of the battery cells increases as the charging rate increases and decreases as the charging rate decreases, and the cell thickness controller has a voltage measurement unit that measures the voltage of each of the battery cells in the cell stack, a cell thickness calculation unit that calculates the cell thickness of the battery cells based on the voltage of the battery cells, and a cell thickness adjustment unit that adjusts the cell thickness of the battery cells.

[0008] According to the battery system (1), cushions are placed in positions where the battery cells of the cell stack come into contact with the battery cells, and the cell thickness of each battery cell of the cell stack is adjustable, so that misalignment of the battery cells can be reduced even if the thickness of the battery cells changes due to charging and discharging. Therefore, even when using battery cells whose cell thickness increases with an increase in the charging rate and decreases with a decrease in the charging rate, the tabs of the battery cells are less likely to bend when connected to the bus bars, and the battery cells themselves are also less likely to bend.

[0009] (2) The battery system described in (1), wherein the cell thickness calculation unit calculates at least one of the charging rate and the deterioration degree of the battery cell from the voltage of the battery cell, and calculates the cell thickness of the battery cell from the obtained at least one of the charging rate and the deterioration degree.

[0010] According to the battery system (2), the cell thickness of each battery cell can be obtained with high precision, and therefore the cell thickness of each battery cell can be adjusted with high precision.

[0011] (3) A battery system described in (1) or (2), wherein the cell thickness adjustment unit charges the battery cell when increasing the cell thickness of the battery cell, and discharges the battery cell when decreasing the cell thickness of the battery cell.

[0012] According to the battery system of (3), the cell thickness of the battery cells is adjusted by charging and discharging the battery cells, so that the cell thickness of each battery cell can be adjusted with higher precision.

[0013] (4) A battery system described in any one of (1) to (3), wherein the battery cell has a pair of tabs, the cell stack has bus bars connected to each of the tabs of the battery cell, the cell thickness calculation unit calculates a positional deviation between the position of the cell side end of the tab and the position of the bus bar side end, and the cell thickness adjustment unit adjusts the cell thickness of the battery cell based on the positional deviation.

[0014] According to the battery system of (4), the cell thickness calculation unit calculates the positional deviation between the cell-side end of the tab and the bus bar-side end, and adjusts the cell thickness of the battery cell based on that positional deviation, thereby minimizing bending of the tab. As a result, the tab of the battery cell connected to the bus bar is less likely to bend, and the battery cell itself is also less likely to bend. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a battery system that uses battery cells whose cell thickness increases as the charging rate increases and decreases as the charging rate decreases, and in which the tabs of the battery cells are less likely to bend when connected to bus bars, and in which the battery cells themselves are also less likely to bend. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram illustrating the configuration of a battery system according to an embodiment of the present invention; [Figure 2] 2 is a schematic diagram showing an example of a charging state of the battery module shown in FIG. 1. FIG. [Figure 3] FIG. 3 is a partially enlarged view of FIG. 2. [Figure 4] 1. FIG. 4 is a schematic diagram showing another example of the charged state of the battery module shown in FIG. [Figure 5] FIG. 5 is a partially enlarged view of FIG. [Figure 6] FIG. 3 is a flow chart illustrating the operation of the battery system according to the embodiment of the present invention. [Figure 7] FIG. 4 is a schematic diagram showing a first modified example of a battery system according to an embodiment of the present invention. [Figure 8] 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

[0017] 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.

[0018] FIG. 1 is a schematic diagram illustrating the configuration of a battery system according to one embodiment of the present invention.

[0019] As shown in FIG. 1 , a battery system 100 of this embodiment includes a battery module 1 and a cell thickness controller 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. Cushions 15 are arranged between the battery cells 11 and between the battery cells 11 and the end plates 17. The cell thickness controller 3 controls the cell thickness of each battery cell 11 in the cell stack 10. The cell thickness controller 3 includes a voltage measurement unit 31, a cell thickness calculation unit 32, and a cell thickness adjustment unit 33. The battery module 1 is housed in a module case 20.

[0020] Each battery cell 11 has a pair of tabs 12. The pair of tabs 12 are arranged on opposing side surfaces, one of which is a positive electrode and the other a negative electrode. Each of the pair of tabs 12 is connected to a bus bar 21. The battery cells 11 located at both ends of the stacking direction of the cell stack 10 are connected to a general terminal bus bar 22. The tabs 12 are arranged so as to be perpendicular to the surface of the bus bar 21 or the general terminal bus bar 22. The bus bar 21 and the general terminal bus bar 22 are housed in a bus bar case 23. The bus bar case 23 is fixed to the module case 20.

[0021] 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 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.

[0022] 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 one of the tabs 12. Examples of materials for 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), 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 Mn2-x-y Examples 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 the other end of the tab 12. Examples of materials for the negative electrode current collector include nickel, copper, and stainless steel. Examples of 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.

[0023] The stacking direction of each layer of the battery cell 11 is the same as the stacking direction of the cell stack 10. Therefore, the thickness of the battery cell 11 changes as the thickness of the negative electrode layer of the battery cell 11 changes.

[0024] Examples of materials for the tabs 12 include copper, copper alloys, aluminum, aluminum alloys, stainless steel, nickel, iron, and titanium. Examples of materials for the bus bars 21 and the main terminal bus bars 22 include copper, copper alloys, aluminum, and aluminum alloys.

[0025] The cushion 15 has the function of alleviating the pressure applied to the battery cells 11 and equalizing the pressure applied to the battery cells 11. For example, a leaf spring or rubber can be used as the cushion 15. For example, a fluid cushion can be used as the cushion 15. The fluid cushion includes an exterior body and a fluid filled inside the exterior body. For example, an aluminum laminate film can be used as the material of the exterior body. The fluid may be a gas or a liquid. For example, nitrogen can be used as the gas. For example, mineral-based hydraulic oil, phosphate ester-based hydraulic oil, water, or a glycol-based solvent can be used as the liquid.

[0026] 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. 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.

[0027] The voltage measurement unit 31 measures the voltage of each battery cell 11 in the cell stack 10. The voltage measurement unit 31 may be, for example, a voltmeter. The voltage measurement unit 31 may measure the internal resistance of the battery cell 11 as well as the voltage of the battery cell 11.

[0028] The cell thickness calculation unit 32 calculates the cell thickness of the battery cell 11 based on the voltage of the battery cell 11 measured by the voltage measurement unit 31. The cell thickness calculation unit 32 may, for example, calculate at least one of the charging rate and the deterioration degree of the battery cell 11 from the voltage of the battery cell 11, and calculate the cell thickness of the battery cell 11 from the obtained charging rate and / or the deterioration degree. The deterioration degree may be calculated using the voltage and internal resistance of the battery cell 11. The cell thickness calculation unit 32 may calculate the positional deviation between the position of the cell-side end of the tab 12 and the position of the busbar-side end. A method for calculating the positional deviation of the tab 12 will be described later.

[0029] The cell thickness adjustment unit 33 adjusts the cell thickness of the battery cell 11 based on the cell thickness of the battery cell 11 calculated by the cell thickness calculation unit 32. For example, the cell thickness adjustment unit 33 charges the battery cell 11 when increasing the cell thickness of the battery cell 11, and discharges the battery cell 11 when decreasing the cell thickness of the battery cell 11.

[0030] Fig. 2 is a schematic diagram showing an example of a charging state of the battery module shown in Fig. 1. Fig. 3 is a partially enlarged view of Fig. 2.

[0031] In the battery module 1a shown in FIG. 2, the thickness of each battery cell 11a increases by the same amount. The increase in the overall cell thickness of the battery cells 11a is offset by the contraction of each cushion 15a. Note that, because the same pressure is applied to each cushion 15a of the battery module 1a, the thickness of each cushion 15a is the same. Because the thickness of each battery cell 11a and the thickness of each cushion 15a are the same, the position of the tab 12 of each battery cell 11a is the same as that of the battery cell 11 before charging. Therefore, as shown in FIG. 3, the position of the cell-side end 12a of the tab 12 is located opposite the busbar-side end 12b, and the cell-side end 12a is not misaligned and is perpendicular to the surface of the busbar 21. In this case, there is no particular need to adjust the cell thickness of the battery cells 11a.

[0032] Fig. 4 is a schematic diagram showing another example of the charged state of the battery module shown in Fig. 1. Fig. 5 is a partially enlarged view of Fig. 4.

[0033] In the battery module 1b shown in FIG. 4, the thickness of each battery cell 11b increases unevenly. The thickness of each cushion 15b is uniform, as in the case of the battery module 1a described above. Therefore, the position of the battery cell 11a shifts from its position before charging. As a result, as shown in FIG. 5, the position of the cell-side end 12a of the tab 12 and the position of the busbar-side end 12b shift, and they do not form a straight line perpendicular to the surface of the busbar 21. In this case, it is necessary to adjust the cell thickness of the battery cell 11b.

[0034] Next, a method for adjusting the cell thickness of the battery cells 11 using the battery system 100 of this embodiment will be described using the battery module 1b shown in Fig. 4 as an example. Fig. 6 is a flow chart illustrating the operation of the battery system according to one embodiment of the present invention.

[0035] First, the SOC (charging rate) and deterioration level of each battery cell 11b of the battery module 1b are measured (S1). This step is performed by the voltage measurement unit 31.

[0036] Next, the cell thickness of each battery cell 11b of the battery module 1b is calculated (S2). This step is performed by the cell thickness calculation unit 32.

[0037] Next, the thickness of each cushion 15b of the battery module 1b is calculated (S3). This step is performed by the cell thickness calculation unit 32. The thickness of the cushion 15b can be calculated by subtracting the total cell thickness of each battery cell 11b from the overall thickness of the cell stack 10 to calculate the total thickness of the cushions 15b, and then dividing the resulting total thickness of the cushions 15b by the number of cushions 15b.

[0038] Next, the position of each cell side end 12a of the tab 12 is calculated (S4). This step is performed by the cell thickness calculation unit 32. The position of each cell side end 12a can be calculated from the cell thickness of each battery cell 11b and the thickness of each cushion 15b.

[0039] Next, the positional deviation between the cell-side end 12a and the busbar-side end 12b of the tab 12 is calculated (S5). This step is performed by the cell thickness calculation unit 32. Because the busbar 21 is housed in the busbar case 23, the position of the busbar-side end 12b of the tab 12 is fixed. Therefore, the positional deviation of the tab 12 is the distance that the cell-side end 12a moves in the thickness direction of the battery cell 11b (the stacking direction of the battery cells 11b) from the position where it faces the busbar-side end 12b.

[0040] Next, the cell thickness of the battery cell 11b is adjusted based on the SOC (state of charge) and the degree of deterioration (S6). This step is performed by the cell thickness adjustment unit 33. By adjusting the cell thickness of the battery cell 11b, the cell-side end 22a of the tab 12 moves along the thickness direction of the battery cell 11b, and the positional deviation between the cell-side end 22a and the busbar-side end 22b of the tab 12 becomes smaller.

[0041] In this way, bending of the tab 12 can be minimized (S7). As a result, bending of the tab 12 makes it less likely that the battery cell 11b connected to the tab will bend, causing deterioration or short-circuiting of the battery cell 11b.

[0042] According to the battery system 100 of this embodiment configured as described above, the cushions 15 are arranged in positions of the cell stack 10 that come into contact with the battery cells 11, and furthermore, the cell thickness is adjustable for each battery cell 11 in the cell stack 10, 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. Therefore, even when using battery cells 11 whose cell thickness increases with an increase in SOC (state of charge) and decreases with a decrease in SOC, the tabs 12 of the battery cells 11 are less likely to bend when connected to the bus bars 21, and the battery cells 11 themselves are also less likely to bend.

[0043] According to the battery system 100 of this embodiment, the cell thickness calculation unit 32 calculates at least one of the charge rate and deterioration degree of the battery cell from the voltage of the battery cell 11, and calculates the cell thickness of the battery cell 11 from the obtained charge rate and / or deterioration degree, thereby obtaining the cell thickness of each battery cell 11 with high accuracy. Therefore, the cell thickness of each battery cell 11 can be adjusted with high accuracy. According to the battery system 100 of this embodiment, the cell thickness adjustment unit 33 charges the battery cell 11 when increasing the cell thickness of the battery cell 11, and discharges the battery cell 11 when decreasing the cell thickness of the battery cell 11, thereby adjusting the cell thickness of each battery cell 11 with high accuracy. According to the battery system 100 of this embodiment, the cell thickness calculation unit 32 calculates the positional deviation between the position of the cell-side end 12a of the tab 12 and the position of the busbar-side end 22b, and the cell thickness adjustment unit 33 adjusts the cell thickness of the battery cell 11 based on the positional deviation, thereby minimizing bending of the tab 12. Therefore, the tabs 12 of the battery cells 11 connected to the bus bars 21 are less likely to bend, and the battery cells 11 themselves are also less likely to bend.

[0044] Although the present invention has been described above in terms of an embodiment, the present invention is not limited to this. For example, in this embodiment, the cushions 15 are disposed between the battery cells 11 and between the battery cells 11 and the end plates 17, but the positions at which the cushions 15 are disposed are not limited to this.

[0045] 7 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, cushions 15 are disposed between the battery cells 11 and the end plates 17, but are 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.

[0046] According to the battery system 100a of the first modification, cushions 15 are disposed between the battery cells 11 and the end plates 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 cushions 15 are not disposed between the battery cells 11, the size of the cell stack 10a can be reduced.

[0047] 8 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 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.

[0048] According to the battery system 100a of the first modification, cushions 15 are placed 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 cushions 15 are not placed between the battery cells 11, the size of the cell stack 10a can be reduced.

[0049] 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 105 to 150.

[0050] In the battery system 100 of this embodiment, a plurality of battery cells 11 are connected in series, but the method of connecting the battery cells 11 is not limited to this. The plurality of battery cells 11 may also be connected in parallel.

[0051] The battery system 100 of this embodiment can be used as a power source for driving a vehicle motor in an electric vehicle, a hybrid electric vehicle (including a plug-in hybrid electric vehicle), etc. The battery system 100 of this embodiment can also be used as a power source for a mobile terminal and as a power storage system for a power generation device. [Explanation of symbols]

[0052] 1 Battery Module 3 Cell Thickness Controller 10, 10a, 10b Cell stack 11 Battery Cells 12 tabs 15 cushions 17 End Plate 20 Module Case 21 Busbar 22 total terminal bus bars 23 Bus Holder 31 Voltage measurement section 32 Cell thickness calculation section 33 Cell thickness adjustment section 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 the stacking direction, with cushions disposed at least either between the battery cells or between the battery cells and the end plates; a cell thickness controller for controlling the cell thickness of each of the battery cells in the cell stack; 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 cell thickness controller includes a voltage measuring unit that measures the voltage of each battery cell of the cell stack, a cell thickness calculating unit that calculates the cell thickness of the battery cell based on the voltage of the battery cell, and a cell thickness adjusting unit that adjusts the cell thickness of the battery cell.

2. 2. The battery system according to claim 1, wherein the cell thickness calculation unit calculates at least one of a charging rate and a deterioration degree of the battery cell from the voltage of the battery cell, and calculates the cell thickness of the battery cell from the obtained at least one of the charging rate and the deterioration degree.

3. 3. The battery system according to claim 1, wherein the cell thickness adjustment unit charges the battery cell when increasing the cell thickness of the battery cell, and discharges the battery cell when decreasing the cell thickness of the battery cell.

4. The battery cell has a pair of tabs, the cell stack has bus bars connecting to the tabs of the battery cells, the cell thickness calculation unit calculates a positional deviation between a position of a cell side end of the tab and a position of a bus bar side end of the tab; The battery system according to claim 1 , wherein the cell thickness adjusting unit adjusts the cell thickness of the battery cell based on the positional deviation.

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