Method for determining reserved gap of battery cell and battery pack

Abstract

The invention relates to the field of battery module reserved gap testing, in particular to a battery cell reserved gap determination method and a battery pack. According to the determination method, a battery cell is circulated without external pressure, and the thickness change corresponding to the battery cell circulation diving inflection point position is tested; the reasonability of the design width of the reserved gap of the battery cell is verified through the numerical value of the thickness change, and a method for determining the size of the reserved gap is provided; the method for determining the reserved gap of the battery cell has the advantages that the test accuracy is high, the judgment method is simple, the design width of the reserved gap of the battery cell can be quickly found, and it is guaranteed that the expansion force and the service life of the battery cell in a designed module are both within a controllable range, the module design time can be shortened, and the use safety and stability of the battery module are guaranteed; the reserved gap of the battery pack is determined through the method for determining the reserved gap of the battery cell, so that the cycle life of the battery pack is prolonged, and the stability of the battery pack is improved.

Description

Technical Field

[0001] The present invention relates to the field of battery module reserved gap testing, and in particular to a method for determining a battery cell reserved gap and a battery pack. Background Art

[0002] During the cycle attenuation process of lithium batteries, the thickness of the battery cell will continue to increase due to side reactions such as the growth of the SEI film and gas production. Reasonable reservation of a certain amount of space can extend the cycle life of the battery cell and reduce the overall expansion force of the module. Excessive reserved space will lead to poor contact between the battery cell electrodes, thereby causing a decrease in the cycle life of the battery cell. Reasonable setting of the reserved gap for the battery cells in the battery module can optimize the performance of the battery module and improve its safety, stability and life.

[0003] Currently, the method for testing the reserved gap of battery cells is to clamp the battery cells with a constant pressure tool, and use a displacement sensor to test the thickness increase of the battery cells throughout their life cycle while ensuring a constant pressure throughout the life cycle of the battery cells, so as to obtain the maximum gap allowed for the battery cells under constant pressure conditions; however, the gap size obtained by the test method under constant pressure conditions is the gap value under constant pressure conditions; in actual situations, after the battery cells are set with a reserved gap in the battery module, there is no constant pressure condition for the battery cells in the initial state, and the pressure on the battery cells gradually changes with the expansion process of the battery cells, resulting in the reserved gap value obtained under constant pressure conditions cannot be used as the accurate value of the reserved gap of the battery cells. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiency in the prior art that the size of the reserved gap of a battery cell cannot be accurately obtained, and to provide a method for determining the reserved gap of a battery cell and a battery pack.

[0005] The present invention provides a method for determining a reserved gap of a battery cell, comprising the following steps: S1: Perform charging cycle test: Perform charging cycle test on the free-state battery cell; The free-state battery cell is a battery cell in an unpressurized state; the unpressurized state of the battery cell is the same as the initial state of the battery cell placed in the battery box, and can better reflect the actual changes of the battery cell in the battery box, so that the obtained battery cell expansion displacement data is the same as the actual displacement of the battery cell in the battery box; the test battery cell is always kept in an unpressurized state, simulating the situation where the gap reserved for the battery cell in the battery box is too large; S2: Record the battery cell status data: record the expansion displacement data of the battery cell in each charging cycle, and record the capacity data of the battery cell in each charging cycle; The expansion displacement data and capacity data of the battery cell are recorded multiple times in each charging cycle.

[0006] S3: Determine the cell capacity drop point: Based on the cell status data in S2, draw a "cycle number-capacity attenuation change rate" chart of the cell to determine the cell capacity drop point; By drawing a "number of cycles-capacity attenuation change rate" chart of the battery cell and taking the point with the obvious capacity attenuation change rate as the battery cell capacity diving point, the battery cell capacity diving point can be determined more intuitively.

[0007] S4: Determine the expansion displacement of the battery cell: Determine the expansion displacement of the free-state battery cell at the capacity diving point according to the battery cell state data in S2, and use the expansion displacement as the expansion gap width d max ; Get the expansion gap width of the battery cell in the free state as the maximum expansion gap width of the battery cell, and obtain the optimal gap width range of the battery cell as 0-d max .

[0008] S5: Verify the allowable gap width: The expansion gap width d max Continue to reduce and obtain the allowable gap width L1, L2, L3...L n ; The allowable gap widths L1, L2, L3...L are set at a fixed number of charging cycles. n The cells are subjected to steps S2-S3 to obtain the allowable gap widths L1, L2, L3, ... L n The capacity dive point below.

[0009] Use different allowable gap widths to perform charging cycle tests on the battery cells and obtain multiple sets of verification data; by comparing and verifying the position of the capacity drop point, the different allowable gap widths L1, L2, L3...L n Verification.

[0010] S6: Determine the reserved gap L of the battery cell: by comparing the allowable gap widths L1, L2, L3...L n The capacity diving point position under the condition of ΔT is obtained to obtain the optimal allowable gap width as the reserved gap L of the battery cell.

[0011] Taking advantage of the characteristic that applying pressure to the battery cell will cause the verification capacity diving point of the battery cell to move backward, multiple groups of verification data are compared to obtain the optimal allowable gap width as the battery cell reserved gap L.

[0012] A method for determining a reserved gap of a battery cell of the present invention can test the battery cell under the condition of the reserved gap in an equivalent module, so that the obtained test data better matches the design of the module; it can quickly find the allowable gap width; it can more accurately test the reserved gap value; by subjecting the battery cell to a charging cycle test without external pressure, the test data of the battery cell can accurately reflect the thickness change of the test battery cell corresponding to the position of the battery cell capacity diving point, and a better design width of the reserved gap of the battery cell is obtained by calculating, adjusting and verifying the thickness change of the battery cell.

[0013] Preferably, in step S5, the fixed number of charging cycles is: the number of charging cycles at the free-state battery cell capacity drop point plus 500.

[0014] Carrying out charging cycle test with fixed cycle number can shorten the test time and facilitate to find the allowable gap width of battery cells that meets the requirements of fixed test cycle number quickly. If the verification battery cells can increase the number of charging cycles by 500 cycles without diving under the number of free-state battery cells diving, it proves that the battery cells have not dived due to excessive gap, and further indicates that the set allowable gap width is reasonable as the reserved gap of battery cells. If the verification battery cells dive within the number of charging cycles increased by 500 cycles under the number of free-state battery cells diving, it is necessary to continue to adjust the value of the allowable gap width of the battery cells and verify the adjusted allowable gap width again.

[0015] Preferably, in step S5, the value range of the allowable gap width is 0-d max , the expansion gap width d max The continuous reduction method is gradient decreasing.

[0016] The reasonable setting range of the allowable gap width can be quickly determined in a gradient decreasing manner.

[0017] Preferably, the values ​​of the allowable gap widths L1, L2, L3, L4, and L5 are respectively: max , 3 / 4d max , 1 / 2d max , 1 / 4d max , 0mm.

[0018] 1 / 4d max By setting a value of the allowable gap width for the interval value, a reasonable setting range of the allowable gap width can be quickly determined.

[0019] Preferably, in step S6, a "corresponding number of cycles during diving - allowable gap width" curve is drawn, and the value range of the optimal allowable gap width is determined by curve fitting.

[0020] By means of curve fitting, the optimal allowable gap width L of the battery cell can be quickly determined.

[0021] Preferably, in step S4, the method for determining the expansion displacement of the battery cell is: according to the number of charging cycles in which the battery cell is located at the capacity diving point, a "battery cell charge-expansion displacement" chart within the charging cycle where the capacity diving point is located is drawn, and the expansion displacement under the state consistent with the initial charge of the battery cell is found.

[0022] The charging cycle where the capacity diving point of the battery cell is located specifically refers to the charging cycle where the capacity diving point occurs. By drawing a "battery cell charge-expansion displacement" chart, the battery cell expansion displacement corresponding to the case of the same initial charge of the battery cell can be found more quickly. When comparing the expansion displacement of the battery cells, the expansion displacement data of the batteries with the same charge can be compared to avoid deviations in the calculation of the expansion displacement of the battery cells.

[0023] Preferably, in step S2, at least 15 displacement measurement points are evenly distributed on a large surface of the battery cell; and the expansion displacement data is an average value of the expansion displacement data of all the displacement measurement points.

[0024] The 15 positions selected on the large surface of the battery cell cover the thinning area of ​​the battery cell and different symmetrical positions on the battery cell geometric dimensions, which can better reflect the thickness changes in different areas of the core package and make the obtained test results more accurate; the average value test result can eliminate the large displacement caused by lithium deposition or other side reactions at a certain position, and reduce the error of expansion displacement.

[0025] Preferably, in step S3, the method for calculating the capacity decay change rate is: calculating the discharge capacity retention rate data of the charging cycle, and calculating the capacity decay change rate data through the discharge capacity retention rate data of the charging cycle; The discharge capacity retention rate data of each charging cycle is the discharge capacity of each charging cycle divided by the discharge capacity of the first charging cycle; The capacity decay rate data is the first-order derivative of the discharge capacity retention rate data with respect to the number of cycles, and the capacity decay rate data is smoothed.

[0026] Assume that the discharge capacity of the first cycle is Q1, and the discharge capacities of the 2nd to nth cycles are defined as Q2, Q n , then the capacity retention rate of the nth cycle is α n =Q n / Q1; with the number of cycles as the horizontal axis and the capacity retention rate as the vertical axis, plot: number of cycles-capacity retention rate; Capacity attenuation change rate: Find the attenuation change rate k when the number of cycles is n n : Calculation formula: k n =[(α n+1 -α n )+(α n -αn -1)] / 2, calculate the attenuation change rate under different cycle numbers according to the above formula, with the number of cycles as the horizontal axis and the capacity attenuation change rate as the vertical axis, and draw a graph: number of cycles-capacity attenuation change rate.

[0027] Preferably, the flatness of the battery cell used for testing is ≤ 0.3% of the thickness of the battery cell.

[0028] By controlling the initial state of the battery cell to be consistent with the initial state of the battery cell group, the test and verification results are more accurate and can more accurately reflect the expansion of the battery cell in the module; the flatness of the battery cell will affect the actual expansion space of the battery cell and the accuracy of the test results; by controlling the state and flatness of the test battery cell, the test results are more accurate.

[0029] The present invention provides a battery pack, comprising a plurality of battery cells and a battery case, wherein the battery cells are arranged in the battery case, and a spacing D is provided between adjacent battery cells, wherein the spacing D is consistent with a battery cell reserved spacing L obtained by the above-mentioned method for determining a battery cell reserved spacing; the battery case has a side plate, and the spacing L between the side plate and the battery cells is provided.

[0030] A battery pack of the present invention comprises a plurality of battery cells arranged in a battery case, a spacing D being provided between large surfaces of adjacent battery cells, the value of the spacing D being consistent with a battery cell reserved gap L obtained by a method for determining a battery cell reserved gap, and a method for determining a battery cell reserved gap being capable of determining the reserved gap between battery cells, so that the battery cells in the battery case have the battery cell reserved gap L at the spacing between the battery cells, the spacing between the side plates and the battery cells is the battery cell reserved gap L, the capacity drop point of the battery cells is at a reasonable number of charging cycles, and the safety, stability and life of the battery pack are improved.

[0031] Compared with the prior art, the present invention has the following beneficial effects: 1. A method for determining a reserved gap of a battery cell of the present invention can test the battery cell under the condition of the reserved gap in an equivalent module, so that the obtained test data better matches the design of the module; can quickly find the allowable gap width; can more accurately test the reserved gap value; by subjecting the battery cell to a charging cycle test without external pressure, the test data of the battery cell can accurately reflect the thickness change of the test battery cell corresponding to the position of the battery cell capacity diving point, and obtain a better design width of the reserved gap of the battery cell by calculating, adjusting and verifying the thickness change of the battery cell.

[0032] 2. A battery pack of the present invention comprises a plurality of battery cells arranged in a battery case, and a spacing D is provided between large surfaces of adjacent battery cells, wherein the value of the spacing D is consistent with a battery cell reserved gap L obtained by a method for determining a battery cell reserved gap. The method for determining a battery cell reserved gap can be used to determine the reserved gap between battery cells, so that the battery cell spacing in the battery case is the battery cell reserved gap L, the spacing between the side plate and the battery cell is the battery cell reserved gap L, the capacity drop point of the battery cell is at a reasonable number of charging cycles, and the safety, stability and life of the battery pack are improved.

[0033] 3. The method for determining the reserved gap of a battery cell of the present invention has high test accuracy and a simple determination method, and can quickly find the design width of the reserved gap of the battery cell, thereby ensuring that the expansion force and life of the battery cell in the designed module are within a controllable range, thereby improving the design efficiency of the battery module, ensuring the safe use of the battery module, and having good economic value and practical value. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 A schematic flow chart of a method for determining a reserved gap for a battery cell; Figure 2 It is a structural schematic diagram of a gap displacement testing device; Figure 3 This is a schematic diagram of the use status of the test cell of the gap displacement test device; Figure 4 This is a schematic diagram of the use status of the verification cell of the gap displacement test device; Figure 5 It is a schematic diagram of the setting state of the filling plate of the gap displacement test device; Figure 6 This is a chart of “cycle number-capacity retention rate”; Figure 7 This is a chart of “number of cycles-capacity attenuation change rate”; Figure 8 It is the curve fitting diagram of Example 2; Fig. 9 This is a schematic diagram of the structure of the liquid cooling plate of Example 3.

[0035] Markings in the figure: 1-frame, 2-bottom plate, 3-push plate, 4-limiting groove, 5-limiting member, 6-displacement sensor, 7-testing battery cell, 8-filling plate, 9-verifying battery cell, 10-battery cell installation groove, 11-liquid cooling plate, 12-limiting part, 13-buffer. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with specific embodiments. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies realized based on the content of the present invention belong to the scope of the present invention.

[0037] Unless otherwise specified, in the description of the specific embodiments of the present invention, the terms indicating the orientation or position relationship such as "up", "down", "left", "right", "center", "inside", "outside", etc. are all based on the expression of the orientation or position relationship shown in the drawings, or are the orientation or position relationship when the invented product / equipment / device is usually used. These terms of orientation or position relationship are only for the convenience of describing the scheme of the present invention or simplifying the description in the specific embodiments, so as to facilitate the technicians to quickly understand the scheme, and do not indicate or imply that a specific device / component / element must have a specific orientation, or be constructed and operated in a specific position relationship, and therefore cannot be understood as a limitation on the present invention.

[0038] In addition, if the terms "horizontal", "vertical", "overhanging", "parallel" and the like appear, it does not mean that the corresponding devices / components / elements are required to be absolutely horizontal or vertical or overhanging or parallel, but may be slightly tilted or have deviations. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but may be slightly tilted. Alternatively, it can be simplified to mean that the corresponding devices / components / elements are set in directions such as "horizontal", "vertical", "overhanging", "parallel", etc., and can have an error / deviation of ±10% relative to the corresponding direction setting, more preferably an error / deviation within ±8%, more preferably an error / deviation within ±6%, more preferably an error / deviation within ±5%, and more preferably an error / deviation within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its role in the scheme of the present invention.

[0039] In addition, the expressions “first”, “second”, “third”, etc., which appear in the terms, are merely used to distinguish the description of the same or similar components and should not be understood as emphasizing or implying the relative importance of specific components.

[0040] In addition, in the description of the embodiments of the present invention, "several", "plurality" and "a number" represent at least 2. It can be any number such as 2, 3, 4, 5, 6, 7, 8, 9, and even more than 9.

[0041] In addition, in the description of the technical solution of the present invention, unless otherwise clearly specified / defined / restricted, the terms "set", "install", "connect", "connected", "provided with", "laid", and "arranged" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection, and can be welding, riveting, bolting, threading, and other commonly used connection means in the field. This connection can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection, or an indirect connection through an intermediate medium, and it can be the internal connection of two elements.

[0042] Example 1 like Figure 1-Figure 7 As shown, a method for determining a reserved gap of a battery cell comprises the following steps: S1: Perform charging cycle test: Perform charging cycle test on the battery cells in a free state; the battery cells are tested in a free state without pressure, which can simulate the actual use state of the battery cells in the battery module; S2: Recording the cell status data: When the cell is not under pressure, perform a charging cycle test on the cell, measure the expansion displacement of the large surface of the cell, record the expansion displacement data of the cell in each charging cycle, and record the capacity data of the cell in each charging cycle; the recorded expansion displacement data and capacity data should correspond to each other with reference to the same time; S3: Determine the cell capacity diving point: Draw a "cycle number-capacity attenuation change rate" chart of the test cell according to the data recorded in S2, take the point where the capacity attenuation change rate changes significantly as the capacity diving point, and obtain the number of charging cycles at which the cell is at the capacity diving point; S4: Determine the expansion displacement of the battery cell: Determine the expansion displacement of the test battery cell at the capacity diving point according to the number of charging cycles at which the test battery cell in S3 is at the capacity diving point; the expansion displacement of the free-state battery cell at the capacity diving point is taken as the maximum expansion gap width d of the battery cell max , based on the maximum expansion gap width d of the battery cell max Determine the allowable gap width of the battery cell; the allowable gap width in the module reflects the gap between the battery cells and the gap between the battery cell and the side wall of the battery box.

[0043] S5: Verify the allowable gap width: Use a gradient decreasing method to determine the allowable gap widths L1, L2, L3...L n The value of the allowable gap width ranges from 0 mm to d max mm; Under the condition of limiting the allowable gap width of the battery cell, replace the battery cell and repeat steps S2-S3 to obtain the allowable gap width L1, L2, L3...L n The capacity diving point under the condition of the first limiting plate and the second limiting plate are set, and the spacing between the first limiting plate and the second limiting plate = the allowable gap width + the thickness of the verification battery cell, and the battery cell is set between the first limiting plate and the second limiting plate; the number of charging cycles of the free battery cell at the capacity diving point + 500 cycles is taken as the number of charging cycles, and the verification battery cell is subjected to a fixed number of charging cycles. The "number of cycles-capacity attenuation change rate" chart of the verification battery cell is drawn to determine the capacity diving point position of the verification battery cell; the allowable gap width L1, L2, L3, ... L of the battery cell is obtained by continuously reducing the value of the gradient decrease to 0.2mm. n, L2 is 0.2mm smaller than L1, L3 is 0.2mm smaller than L2, and the value of the gradient decrease can be set to 0.3mm, 0.4mm... Selecting an appropriate value of the gradient decrease can quickly determine the optimal allowable gap width; S6: Determine the reserved gap L for the battery cells: respectively determine the allowable gap widths L1, L2, L3...L n The allowable gap is verified, and the optimal allowable gap width is obtained as the reserved gap L of the battery cell by comparing the diving point positions corresponding to different allowable gap widths.

[0044] Specifically, the battery cell subjected to the charging cycle test in the free state is the test battery cell, and the obtained capacity diving point is the test capacity diving point; the battery cell used to verify the allowable gap width is the verification battery cell, and the obtained capacity diving point is the verification capacity diving point; the test battery cell and the verification battery cell both have a battery cell large surface, and the test battery cell and the verification battery cell are batteries of the same type and specification.

[0045] A method for determining a reserved gap of a battery cell of the present invention can test the battery cell under the condition of the reserved gap in an equivalent module, so that the obtained test data better matches the design of the module; can quickly find the allowable gap width; can more accurately test the reserved gap value; by subjecting the battery cell to a charging cycle test without external pressure, the test data of the battery cell can accurately reflect the thickness change of the test battery cell corresponding to the position of the battery cell capacity diving point, and calculate, verify and adjust the allowable gap width of the battery cell according to the thickness change of the battery cell, so as to obtain a more suitable design width of the reserved gap of the battery cell.

[0046] The test cell is a square or soft-pack cell. The SOC state of the test cell is required to be consistent with that of the cell when grouped. The flatness of the test cell is required to be ≤ 0.3% of the total thickness of the test cell. The flatness of the verification cell is required to be ≤ 0.3% of the total thickness of the verification cell.

[0047] The method for determining the reserved gap of the battery cell is as follows: Figure 2-Figure 5The gap displacement testing device shown in the figure is carried out, and the gap displacement testing device is composed of a frame 1, a base plate 2 and a push plate 3. The base plate 2 and the push plate 3 are arranged opposite to each other, and the base plate 2 is fixedly connected to the frame 1. The base plate 2 is provided with a limiting groove 4, and the push plate 3 is slidably arranged on the frame 1. The push plate 3 is provided with a limiting member 5, and the limiting member 5 is used to fix the distance between the push plate 3 and the base plate 2. A plurality of through mounting holes are opened on the base plate 2, and a displacement sensor 6 can be arranged in the mounting hole. The displacement sensor 6 can be adjusted relative to the mounting hole so that the displacement sensor 6 can abut against the battery cell; the gap displacement testing device can realize the limitation and positioning of the battery cell, and by sliding the push plate 3 on the frame 1, the distance between the push plate 3 and the base plate 2 can be adjusted, and the limiting member 5 can fix the push plate 3 at a predetermined position so that the distance between the base plate 2 and the push plate 3 remains unchanged; the displacement sensor 6 is A pen-shaped sensor is provided with a cell mounting groove 10 on the push plate 3, a limiting groove 4 is opened at the bottom of the cell mounting groove 10, a displacement sensor 6 passes through the bottom of the limiting groove 4, and the cell mounting groove 10 can be adapted to the shapes of the test cell 7 and the verification cell 9 respectively; the cell mounting groove 10 is provided in plurality, and the plurality of cell mounting grooves 10 are opened in sequence from large to small, the smaller cell mounting groove 10 is opened at the bottom of the larger cell mounting groove 10, and the limiting groove 4 is opened at the bottom of the smallest cell mounting groove 10; cell mounting grooves 10 of different sizes are used to limit cells of different specifications, so that the gap displacement test device can be used to test cells of different specifications, ensuring that the test cell 7 is subjected to a charging cycle test in a free state; when the verification cell 9 expands, the cell large surface of the verification cell 9 can continuously shorten the distance between it and the push plate 3 until the cell large surface abuts against the push plate 3.

[0048] Specifically, the test cell 7 is arranged between the bottom plate 2 and the push plate 3, the bottom plate 2 is provided with a displacement sensor 6, the large surface of the test cell 7 abuts the displacement sensor 6, and the side opposite to the large surface of the cell abuts the push plate 3; so that there is no gap between the test cell 7 and the push plate 3; a displacement gap of the test cell 7 is set between the test cell 7 and the bottom plate 2, the displacement gap is 10%-15% of the thickness of the test cell 7, and the width of the displacement gap is usually 6-8mm; before performing the cell charging cycle process, the displacement sensor 6 is zeroed and the displacement sensor 6 is in contact with the large surface of the test cell 7; the displacement gap exceeds the maximum gap that can be reserved in the module design, ensuring that the test cell 7 has sufficient space to expand and a capacity dive occurs.

[0049] Specifically, in S5, the verification cell 9 is arranged between the bottom plate 2 and the push plate 3, the push plate 3 serves as the first limiting plate, the bottom plate 2 serves as the second limiting plate, the filling plate 8 is arranged in the limiting groove 4, and the cell installation groove 10 serves as the cell clamping groove to limit the verification cell 9, so that one side of the verification cell 9 abuts against the bottom plate 2. The filling plate 8 is a sheet metal plate, and the shape of the filling plate 8 is adapted to the shape of the limiting groove 4. After the filling plate 8 is installed, the filling plate 8 and the push plate 3 are two mutually parallel planes arranged facing each other, so as to ensure that the cell can be squeezed by the push plate 3 and the filling plate 8 after expansion.

[0050] In one or more embodiments, the method for determining the expansion displacement of the cell at the capacity diving point is as follows: according to the number of charging cycles when the cell is at the capacity diving point, a "cell charge-expansion displacement" chart is drawn within the charging cycle where the cell capacity diving point is located, and the expansion displacement corresponding to the case where the initial charge of the test cell 7 is consistent is found. Drawing the "cell capacity-expansion displacement" chart within the charging cycle where the cell capacity diving point is located can quickly find the cell capacity diving point, and only the charging cycle where the cell capacity diving point is located is graphed, which reduces the amount of data processing, enables the operator to quickly complete the confirmation of the expansion displacement of the cell at the capacity diving point, and improves the work efficiency; accurately determines the expansion displacement at the capacity diving point, and ensures the accuracy of subsequent calculation results.

[0051] In one or more embodiments, the expansion displacement of the large surface of the battery cell is measured at the end of charging, or the expansion displacement of the large surface of the battery cell is measured at the end of discharging; in some embodiments, a node of any SOC state of the battery cell can be selected to measure the expansion displacement of the large surface of the battery cell, and it is necessary to ensure that the SOC state of the battery cell during each measurement cycle is consistent with the selected SOC state.

[0052] Specifically, the initial thickness of the test cell is 50.6 mm, the initial SOC state is 30%, and the test cell is in a free state without stress, thereby simulating the situation where the reserved gap of the cell in the battery module is set too large.

[0053] It is found that the capacity of the test cell drops at 277 cycles, and the displacement increment of the test cell at 30% SOC at 277 cycles is 7.74 mm, so d max The value is 7.74mm In one or more embodiments, at least 15 evenly distributed displacement measurement points are set on the large surface of the test cell 7; the expansion displacement of the test cell 7 is the average of the expansion displacements of all displacement measurement points. After the installation position of the test cell 7 is determined, a displacement sensor 6 is installed on the bottom plate 2: a displacement sensor 6 is set at a position 5mm from the left edge of the core package, 1 / 4 position, 1 / 2 position, 3 / 4 position, and 5mm from the right edge of the core package on the large surface of the cell from left to right; a displacement sensor 6 is set at a position 5mm from the top of the core package, 1 / 4 position, 1 / 2 position, 3 / 4 position, and 5mm from the bottom edge of the core package on the large surface of the cell from top to bottom. The total number of test points is ≥15. The above positions cover the cell thinning area and the different symmetrical positions of the cell in the entire geometric size, which can better reflect the thickness changes in different areas of the core package and make the test results more accurate.

[0054] In one or more embodiments, the method for calculating the capacity decay change rate is as follows: first, calculate the discharge capacity retention rate data of each charging cycle, the discharge capacity retention rate data of each charging cycle = the discharge capacity of each charging cycle divided by the discharge capacity of the first charging cycle; the capacity decay change rate data = the first-order derivative of the discharge capacity retention rate data with respect to the number of cycles, and smooth the capacity decay change rate data. Assume that the discharge capacity of the first cycle is Q1, and the discharge capacities of the 2nd to nth cycles are defined as Q2, Q n , then the capacity retention rate of the nth cycle is α n =Q n / Q1; With the number of cycles as the horizontal axis and the capacity retention rate as the vertical axis, draw a graph: number of cycles - capacity retention rate; capacity attenuation change rate: calculate the attenuation change rate k when the number of cycles is n n : Calculation formula: k n =[(α n+1 -α n )+( α n -α n-1 )] / 2, calculate the attenuation change rate under different cycle numbers according to the above formula, with the number of cycles as the horizontal axis and the capacity attenuation change rate as the vertical axis, and draw a graph: number of cycles-capacity attenuation change rate; Specifically, the capacity retention rate and attenuation rate of the test cells at different cycle times are as follows In one or more embodiments, in S2, a "cycle number-capacity retention rate" chart is drawn to assist in determining the capacity drop point of the test battery cell 7.

[0055] In a specific implementation, a cyclic test is performed to obtain the allowable gap width of the battery cell: the spacing between the bottom plate 2 and the push plate 3 on the gap displacement testing device is adjusted so that the spacing between the bottom plate 2 and the push plate 3 is 10%-15% of the thickness of the test battery cell 7, and the position between the bottom plate 2 and the push plate 3 is fixed by using the limiter 5; the test battery cell 7 is placed between the bottom plate 2 and the push plate 3 so that the test battery cell 7 is in contact with the push plate 3, and a displacement sensor 6 is arranged in a number of through holes in the bottom plate 2 so that the end of the displacement sensor 6 is in contact with the large surface of the test battery cell 7, and the position of the displacement sensor 6 is adjusted so that the displacement sensor 6 is in contact with the test battery cell 7 in the initial state without applying force to the test battery cell 7, and the displacement sensor 6 is zeroed; the displacement sensor 6 is set to 15, and the displacement sensors 6 are arranged from left to right on the large surface of the battery cell at a position 5mm away from the left edge of the core package, a position 1 / 4 of the core package, a position 1 / 2 of the core package, a position 3 / 4 of the core package, and a position 5mm away from the right edge of the core package, and the displacement sensors 6 are arranged at the large surface of the battery cell according to the position of the displacement sensor 6 on the large surface of the battery cell. From top to bottom, a displacement sensor 6 is set at a position 5 mm away from the top of the core package, a position 1 / 4, a position 1 / 2, a position 3 / 4 away from the top of the core package, and a position 5 mm away from the edge of the bottom core package, so that the displacement sensor 6 can more accurately reflect the expansion displacement of the test cell 7 during the charging cycle; the test cell 7 is charged and discharged, and the maximum capacity of the cell charged in each charging cycle of the test cell 7 and the cell expansion displacement when the cell capacity reaches the initial charging capacity in each charging cycle of the test cell 7 are recorded, and the "number of cycles-capacity attenuation change rate" chart and the "number of cycles-capacity retention rate" chart are recorded. The capacity diving point of the test cell 7 is judged by the "number of cycles-capacity attenuation change rate" chart, the "number of cycles-capacity retention rate" chart, and the "cell capacity-expansion displacement" chart, and the charging cycle number where the capacity diving point of the test cell 7 is located and the cell expansion displacement at the capacity diving point of the test cell 7 are obtained, so as to obtain the maximum expansion gap width d of the cell. max , and continuously reduce the allowable gap width L1, L2, L3, etc. of the battery cell to a fixed value of 0.2 mm. n , L2 is 0.2 mm smaller than L1, L3 is 0.2 mm smaller than L2, and so on to obtain multiple allowable gap width data.

[0056] Verify whether the allowable gap width is set reasonably: remove all displacement sensors 6, set a sheet metal part as a filling plate 8 in the limit groove 4 of the bottom plate 2, make the two opposite planes of the filling plate 8 and the push plate 3 parallel, adjust the distance between the push plate 3 and the filling plate 8 to the allowable gap width of the battery cell, and when setting the verification battery cell 9, turn the large surface of the verification battery cell 9 toward the push plate 3 or the filling plate 8, so that the verification battery cell 9 is clamped in the battery cell installation groove 10, and simulate the reserved gap in the battery module through the push plate 3 and the large surface of the battery cell; perform a charging cycle test on the verification battery cell 9, and perform a charging cycle test on the verification battery cell 9 with a fixed number of cycles as the target of the number of cycles + 500 cycles of the capacity diving point of the test battery cell 7, and draw a "number of cycles-capacity attenuation change rate" chart of the verification battery cell 9 to determine the capacity diving point of the verification battery cell 9; use the allowable gap widths L1, L2, L3...L respectively n The battery cell is verified; by comparing the diving point positions corresponding to different allowable gap widths, the optimal allowable gap width is obtained as the reserved gap of the battery cell; the optimal allowable gap width is: among the allowable gap width values ​​without capacity diving within the number of cycles of the test battery cell 7 capacity diving points + 500 charging cycles, the maximum value is taken as the optimal value.

[0057] Example 2 The implementation process of the method for determining the reserved gap of a battery cell in this embodiment is substantially the same as that of the embodiment 1. The difference from the embodiment 1 is that the allowable gap widths L1, L2, L3, ... L n The value is: d max , 3 / 4d max , 1 / 2d max , 1 / 4d max , 0mm; 1 / 4d max The change gradient determines the allowable gap widths L1, L2, L3...L n The value of can quickly determine the setting range of the optimal allowable gap width L, which can reduce the number of verification experiments. In addition to the boundary values, there are 3 sets of intermediate values, which can meet the minimum number requirements for trend prediction.

[0058] Under the condition of initial preload of 3000N, the test data of the battery cell with initial thickness of 50.6mm under different gap settings are as follows Among them, 1 / 4d max 1% of the cell thickness, 1 / 2d max 2% of the cell thickness, 3 / 4d max 4% of the cell thickness, 3 / 4d max is 8% of the cell thickness, d maxTake a value close to the percentage of the battery cell thickness, with the minimum value accurate to 0.5%; the initial preload range is 100N-5000N, and the initial preload of 3000N is set according to the typical preload value used in module or system assembly; the fixture stiffness satisfies the strain under 2Mpa stress <0.2mm; the expansion force under 90%SOH shows that the larger the battery cell gap under the same SOH, the smaller the corresponding expansion force value, and the battery cell cycle expansion force can be reduced by increasing the gap.

[0059] In a specific embodiment, Figure 8 As shown, in S6, a "corresponding number of cycles during diving - allowable gap width" curve is drawn, and the optimal allowable gap width of the battery cell is determined by curve fitting; the curve fitting can quickly find that the range of the value of the optimal allowable gap width is about 3% of the battery cell thickness.

[0060] Specifically, based on the balance between the maximum expansion force that the system can withstand and the cycle life, the reserved gap L of the battery cell can be designed to be 2%~4% of the battery cell thickness; based on the difference in the design group margin of the battery cell itself, the reserved gap L of the battery cell can be designed to be 0%~5% of the battery cell thickness.

[0061] Example 3 A battery pack of the present embodiment includes a plurality of battery cells and a battery case, wherein the battery cells are arranged in the battery case, and a spacing D is provided between adjacent battery cells, wherein the spacing D is consistent with a battery cell reserved spacing L obtained by a method for determining a battery cell reserved spacing in Example 2, that is, D=L; the battery case has a side panel, and a spacing L between the side panel and the battery cells.

[0062] Specifically, the battery box is a rectangular box, which is composed of a bottom plate and four side plates. The four side plates are connected to each other, and the bottoms of the four side plates are connected to the bottom plate, thereby forming a rectangular accommodating space for accommodating battery cells. A number of battery cells with an initial thickness of 50.6 mm are arranged in the accommodating space. The spacing between adjacent battery cells is 2% of the battery cell thickness, that is, 1.012 mm, and the distance between the battery cell closest to the side plate and the side plate is 1.012 mm.

[0063] In an optional implementation, the reserved gap L of the battery cell is 0% to 5% of the thickness of the battery cell.

[0064] In one or more embodiments, a frame structure is provided on the base plate, and the battery cells are embedded in the frame structure by adapting to control the distance between adjacent battery cells, ensuring that the spacing between the battery cells is a preset value L. The height of the frame structure is less than 2 mm to avoid applying additional pre-tightening force to the bottom of the battery cell, and at the same time, the overflow of the thermal conductive structural adhesive at the bottom of the battery cell can be limited.

[0065] like Fig. 9As shown, in an optional embodiment, a liquid cooling plate 11 is provided on the bottom plate, and a plurality of limiting portions 12 are provided on the liquid cooling plate 11. The limiting portions 12 are arranged in strips on the top of the liquid cooling plate 11, and adjacent limiting portions 12 are parallel to each other. The spacing between adjacent limiting portions 12 is consistent with the thickness of the battery cell, so that the battery cell can be clamped between adjacent limiting portions 12, and the height of the limiting portion 12 is less than 2 mm.

[0066] Specifically, a buffer 13 is arranged between adjacent battery cells. The buffer 13 is arranged on the top of the limiting portion 12. The buffer 13 is a buffer PP circular frame. In some embodiments, the buffer 13 can also be a PP strip, a silicone strip, a silicone frame, XPP foam, aerogel, etc.

[0067] A battery pack of this embodiment solves the problem of mechanical structure failure and poor cycle life caused by excessive expansion force of the battery system, and is suitable for the design of a long-life, low-expansion battery system for all square and soft-pack batteries.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining the reserved gap of a battery cell, It is characterized in that The steps include: S1: Perform charging cycle test: Perform charging cycle test on the free-state battery cell; S2: Record the battery cell status data: record the expansion displacement data of the battery cell in each charging cycle, and record the capacity data of the battery cell in each charging cycle; S3: Determine the cell capacity drop point: Based on the cell status data in S2, draw a "cycle number-capacity attenuation change rate" chart of the cell to determine the cell capacity drop point; S4: Determine the expansion displacement of the battery cell: Determine the expansion displacement of the free-state battery cell at the capacity diving point according to the battery cell state data in S2, and use the expansion displacement as the expansion gap width d max ; S5: Verify the allowable gap width: The expansion gap width d max Continue to reduce and obtain the allowable gap width L 1 , L 2 , L 3 ...L n ; The allowable gap width L is set at a fixed number of charging cycles. 1 , L 2 , L 3 ...L n The cells are subjected to steps S2-S3 to obtain the allowable gap width L 1 , L 2 , L 3 ...L n The capacity dive point below; S6: Determine the reserved gap L for the battery cell: by comparing the allowable gap width L 1 , L 2 , L 3 ...L n The capacity diving point position under the condition of ΔT is obtained to obtain the optimal allowable gap width as the reserved gap L of the battery cell.

2. A method for determining a reserved gap of a battery cell according to claim 1, It is characterized in that In step S5, the fixed number of charging cycles is: the number of charging cycles at the free-state battery cell capacity drop point plus 500.

3. A method for determining a reserved gap of a battery cell according to claim 1, It is characterized in that In step S5, the range of the allowable gap width is 0-d max , the expansion gap width d max The continuous reduction method is gradient decreasing.

4. A method for determining a reserved gap of a battery cell according to claim 3, It is characterized in that The allowable gap width L 1 , L 2 , L 3 , L 4 , L 5 The values ​​are: d max , 3 / 4d max , 1 / 2d max , 1 / 4d max , 0mm.

5. A method for determining a reserved gap of a battery cell according to claim 3, It is characterized in that In step S6, a "corresponding number of cycles during diving - allowable gap width" curve is drawn, and the value range of the optimal allowable gap width is determined by curve fitting.

6. A method for determining a reserved gap of a battery cell according to claim 1, It is characterized in that In step S4, the method for determining the expansion displacement of the battery cell is: according to the number of charging cycles in which the battery cell is located at the capacity diving point, a "battery cell charge-expansion displacement" chart within the charging cycle where the capacity diving point is located is drawn, and the expansion displacement in a state consistent with the initial charge of the battery cell is found.

7. A method for determining a reserved gap of a battery cell according to claim 1, It is characterized in that In step S2, at least 15 displacement measurement points are evenly distributed on the large surface of the battery cell; the expansion displacement data is the average value of the expansion displacement data of all the displacement measurement points.

8. A method for determining a reserved gap of a battery cell according to claim 1, It is characterized in that In step S3, the method for calculating the capacity decay change rate is: calculating the discharge capacity retention rate data of the charging cycle, and calculating the capacity decay change rate data through the discharge capacity retention rate data of the charging cycle; The discharge capacity retention rate data of each charging cycle is the discharge capacity of each charging cycle divided by the discharge capacity of the first charging cycle; The capacity decay rate data is the first-order derivative of the discharge capacity retention rate data with respect to the number of cycles, and the capacity decay rate data is smoothed.

9. A method for determining a reserved gap of a battery cell according to any one of claims 1 to 8, It is characterized in that The flatness of the battery cell used for testing is ≤ 0.3% of the battery cell thickness.

10. A battery pack, It is characterized in that The invention comprises a plurality of battery cells and a battery case, wherein the battery cells are arranged in the battery case, and a spacing D is provided between adjacent battery cells, wherein the spacing D is consistent with a battery cell reserved spacing L obtained by adopting a method for determining a battery cell reserved spacing as described in any one of claims 1 to 9; and the battery case has a side plate, and a spacing L between the side plate and the battery cells.

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