Battery capacity testing method

Abstract

The invention relates to a battery capacity test method, which comprises the following steps of S1, performing six-stage discharge on a standard battery monomer under medium and low charge conditions, and recording charge capacity, static voltage and working voltage in the discharge process; s2, fitting two equations according to the charge capacity and the static voltage; s3, performing two-stage discharge on the to-be-predicted battery, and taking the working voltage as a cut-off condition to obtain the post-standing voltage of the two-stage discharge of the to-be-predicted battery; and S4, calculating the capacity of the battery to be predicted according to a formula. According to the battery capacity prediction method, the battery capacity can be tested without fully charging the battery, the thickness of the battery is not too large, and the working procedure and time of battery capacity testing are both shorter than those of a conventional capacity grading method.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a battery capacity testing method. Background Art

[0002] Capacity is an important performance indicator of lithium-ion batteries. During the later battery assembly, multiple single cells need to be connected in series and parallel to form modules and battery packs. Therefore, how to clearly determine the capacity of battery cells before assembly is a technical problem that needs to be solved urgently in battery technology. Summary of the Invention

[0003] To this end, the present invention provides a battery capacity testing method, which can obtain the capacity of a battery cell while ensuring that the thickness of the battery cell is not affected by the capacity test.

[0004] In order to solve the above technical problems, the present invention provides a battery capacity testing method. The following steps are involved: S1: discharging a fully charged standard battery cell at a fixed rate and constant current to a first state of charge value, controlling the standard battery cell to enter a rest phase, and obtaining a first static voltage of the standard battery cell after the rest phase is completed; Continue to discharge the standard battery cell at a fixed rate constant current to a second state of charge value, and obtain the operating voltage V1 of the standard battery cell at the end of discharge; control the standard battery cell to enter a rest phase, and obtain a second static voltage of the standard battery cell after the rest phase is completed; Continue to discharge the standard battery cell at a fixed rate and constant current to a third state of charge value, control the standard battery cell to enter a rest phase, and obtain a third static voltage of the standard battery cell after the rest phase is completed; Continue to discharge the standard battery cell at a fixed rate and constant current to a fourth state of charge value, control the standard battery cell to enter a rest phase, and obtain a fourth static voltage of the standard battery cell after the rest phase is completed; Continue to discharge the standard battery cell at a fixed rate constant current to a fifth state of charge value, and obtain the operating voltage V2 of the standard battery cell at the end of discharge; control the standard battery cell to enter a rest phase, and obtain the fifth static voltage of the standard battery cell after the rest phase is completed; Continue discharging the standard battery cell at a fixed rate and constant current to a sixth state of charge value, control the standard battery cell to enter a rest phase, and obtain a sixth static voltage of the standard battery cell after the rest phase is completed; S2: With the static voltage as the abscissa and the state of charge value as the ordinate, a linear fit is performed on the first state of charge value, the second state of charge value, the third state of charge value, the first static voltage, the second static voltage, and the third static voltage to obtain a first fitting equation y1=a1x1+b1; with the static voltage as the abscissa and the state of charge value as the ordinate, a linear fit is performed on the fourth state of charge value, the fifth state of charge value, the sixth state of charge value, the fourth static voltage, the fifth static voltage, and the sixth static voltage to obtain a second fitting equation y2=a2x2+b2; S3: Acquire a battery cell to be predicted that is of the same type as the standard battery cell, and make the battery cell to be predicted have an initial voltage V0, where V0>V1; S4: discharging the battery cell to be predicted at a fixed rate and constant current. When the battery cell to be predicted is discharged to the operating voltage V1, discharging is stopped and the battery cell to be predicted is controlled to enter a rest phase. The voltage of the battery cell to be predicted after the rest phase is obtained as V3. S5: Continue to discharge the battery cell to be predicted at a fixed rate and constant current. When the battery cell to be predicted is discharged to the operating voltage V2, stop discharging and obtain the discharge capacity C0 during the discharge period; control the battery cell to be predicted to enter a rest phase, and obtain the voltage of the battery cell to be predicted after the rest phase as V4; S6: According to steps S2-S5 and the formula C=C0÷(y1-y2), C=C0÷[(a1V3+b1)-(a2V4+b2)] is obtained, wherein C is the capacity of the battery cell to be predicted after being fully charged and discharged to the discharge cut-off voltage.

[0005] Furthermore, in step S3, the battery cell to be predicted is a battery cell of the same type as the standard battery cell and has been formed.

[0006] Further, in step S1, the first state of charge value ranges from 11% to 50%; the difference between the second state of charge value and the first state of charge value ranges from 1% to 5%; and the difference between the third state of charge value and the second state of charge value ranges from 1% to 5%.

[0007] Furthermore, in step S1, the fourth state of charge value ranges from 5% to 30%; the difference between the fifth state of charge value and the fourth state of charge value ranges from 1% to 5%; and the difference between the sixth state of charge value and the fifth state of charge value ranges from 1% to 5%.

[0008] Further, in step S1, the value ranges of the first state of charge value and the fourth state of charge value are both between 0% and 20%; or, the value ranges of the first state of charge value and the fourth state of charge value are both between 20% and 50%.

[0009] Further, in step S1, the difference between the second state of charge value and the first state of charge value, the difference between the third state of charge value and the second state of charge value, the difference between the fifth state of charge value and the fourth state of charge value, and the difference between the sixth state of charge value and the fifth state of charge value are all equal.

[0010] Furthermore, in step S1, the fifth state of charge value is 0%, and the operating voltage V2 is the discharge cut-off voltage of the standard battery cell.

[0011] Furthermore, in step S1 , the operating voltage of the standard battery cell when the standard battery cell is discharged at a constant current to a sixth state of charge value is lower than the over-discharge protection voltage of the standard battery cell.

[0012] Furthermore, in step S2, the first fitting equation is y1=1.8634x1-5.8872; the second fitting equation is y2=0.1251x2-0.375.

[0013] Furthermore, in step S3 , the difference between the thickness of the battery cell to be predicted at the initial voltage V0 and the thickness of the battery cell to be predicted before formation is controlled to be within 0.5 mm.

[0014] The above technical solution of the present invention has the following advantages over the prior art: 1) In the battery capacity testing method described herein, since the two fitting equations derived from the linear fitting of a standard battery cell both use the static voltage as the horizontal axis and the state of charge value as the vertical axis, there is no need to fully charge the battery cell to be tested. Instead, the discharge capacity C0 of the battery cell to be tested, measured from an operating voltage V1 to an operating voltage V2, can be used to predict the capacity C of the battery cell to be tested after being fully charged to the discharge cutoff voltage. This solves the problem of battery cell thickening caused by fully charging the battery cell in existing capacity grading processes. Furthermore, compared with existing capacity grading processes, capacity testing is much faster. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings.

[0016] Figure 1 The equation diagram when the first fitting equation is fitted by the present invention; Figure 2 This is an equation diagram when the second fitting equation is fitted by the present invention. DETAILED DESCRIPTION

[0017] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0018] The inventors learned that the current related technology relies on a capacity division process to determine the capacity of the battery cell. Usually, the battery cell is fully charged with constant current and constant voltage in a capacity division cabinet, and then discharged at a certain rate and constant current according to the process or customer requirements after standing for a period of time. After 2-4 complete full charge and discharge cycles, the last full discharge capacity is taken as the capacity division capacity for grading.

[0019] The inventors also learned that in order to pursue long-endurance performance, at the battery cell level, in addition to improving the material itself, it can only be achieved by fully utilizing the overall space. In other words, the group margin of battery cells is often relatively large.

[0020] In this way, the inventors discovered that when the group margin of the battery cell is relatively large, for example, when the group margin is greater than 92%, the battery cell will bulge during the capacity distribution stage, that is, the full charging and discharging stage, because the electrode will expand and there is no space to release the stress, making the battery cell thicker, thereby affecting the subsequent assembly of the battery module or battery pack.

[0021] Therefore, in order to solve the above problems, the present invention proposes a battery capacity testing method, comprising the following steps: S1: discharging a fully charged standard battery cell at a fixed rate and constant current to a first state of charge value, controlling the standard battery cell to enter a rest phase, and obtaining a first static voltage of the standard battery cell after the rest phase, wherein the discharge temperature is 25°C; Continue to discharge the standard battery cell at a fixed rate constant current to a second state of charge value, and obtain the operating voltage V1 of the standard battery cell at the end of discharge; control the standard battery cell to enter a rest phase, and obtain a second static voltage of the standard battery cell after the rest phase is completed; Continue to discharge the standard battery cell at a fixed rate and constant current to a third state of charge value, control the standard battery cell to enter a rest phase, and obtain a third static voltage of the standard battery cell after the rest phase is completed; Continue to discharge the standard battery cell at a fixed rate and constant current to a fourth state of charge value, control the standard battery cell to enter a rest phase, and obtain a fourth static voltage of the standard battery cell after the rest phase is completed; Continue to discharge the standard battery cell at a fixed rate constant current to a fifth state of charge value, and obtain the operating voltage V2 of the standard battery cell at the end of discharge; control the standard battery cell to enter a rest phase, and obtain the fifth static voltage of the standard battery cell after the rest phase is completed; Continue discharging the standard battery cell at a fixed rate and constant current to a sixth state of charge value, control the standard battery cell to enter a rest phase, and obtain a sixth static voltage of the standard battery cell after the rest phase is completed; S2: With the static voltage as the abscissa and the state of charge value as the ordinate, a linear fit is performed on the first state of charge value, the second state of charge value, the third state of charge value, the first static voltage, the second static voltage, and the third static voltage to obtain a first fitting equation y1=a1x1+b1; with the static voltage as the abscissa and the state of charge value as the ordinate, a linear fit is performed on the fourth state of charge value, the fifth state of charge value, the sixth state of charge value, the fourth static voltage, the fifth static voltage, and the sixth static voltage to obtain a second fitting equation y2=a2x2+b2; S3: Acquire a battery cell to be predicted that is of the same type as the standard battery cell, and make the battery cell to be predicted have an initial voltage V0, where V0>V1; S4: discharging the battery cell to be predicted at a fixed rate and constant current. When the battery cell to be predicted is discharged to the operating voltage V1, discharging is stopped and the battery cell to be predicted is controlled to enter a rest phase. The voltage of the battery cell to be predicted after the rest phase is obtained as V3. The discharge temperature is 25°C. S5: Continue to discharge the battery cell to be predicted at a fixed rate and constant current. When the battery cell to be predicted is discharged to the operating voltage V2, stop discharging and obtain the discharge capacity C0 during the discharge period; control the battery cell to be predicted to enter a rest phase, and obtain the voltage of the battery cell to be predicted after the rest phase as V4; S6: According to steps S2-S5 and the formula C=C0÷(y1-y2), C=C0÷[(a1V3+b1)-(a2V4+b2)] is obtained, wherein C is the capacity of the battery cell to be predicted after being fully charged and discharged to the discharge cut-off voltage.

[0022] In this embodiment, in order to solve the problem of battery cell thickness increase caused by full charging of the battery cell in the existing capacity separation process and to facilitate faster capacity testing of the battery cell, two fitting equations are developed using linear fitting of standard battery cells to obtain the relationship between the static voltage and the state of charge value. Furthermore, it is not necessary to fully charge the battery cell to be predicted. Instead, it is only necessary to measure the discharge capacity C0 of the battery cell to be predicted when discharged from the operating voltage V1 to the operating voltage V2. The capacity C of the battery cell to be predicted when discharged to the discharge cut-off voltage after being fully charged can be predicted using the two fitting equations.

[0023] It should be noted that in step S1, the standard battery cells are selected after the capacity determination process. That is to say, for example, the SOC-OCV characteristic curve and discharge characteristic curve of the standard battery cells can be obtained by existing means, and the specific acquisition means will not be repeated here.

[0024] It's also important to note that the state of charge (SOC) refers to the ratio of a battery's current charge to its full capacity. When not charging, the battery's capacity is considered to be A0, corresponding to 0% SOC. When fully charged, the battery is considered to have reached its rated capacity, A, corresponding to 100% SOC. During charging, when the battery's capacity is x% (A-A0), it corresponds to x% SOC, where x% is a value between 0 and 100. For example, if x is 50, the battery is charged to 50% of its capacity (A-A0), corresponding to 50% SOC.

[0025] In some embodiments, in order to improve the accuracy of the two fitting equations linearly fitted in step S2, multiple standard battery cells are designed, the capacity consistency of the multiple standard battery cells is high, and each standard battery cell undergoes step S1, and after taking the average value of the first to sixth static voltages of the multiple standard battery cells, step S2 is performed to fit the first fitting equation and the second fitting equation respectively.

[0026] In some embodiments, in order to ensure that the thickness of the battery cell to be predicted in step S3 when it has an initial voltage V0 does not affect the subsequent assembly of the battery module or battery pack, the thickness of the battery cell to be predicted when it has an initial voltage V0 is limited, that is, the difference between the thickness of the battery cell to be predicted at the initial voltage V0 and the thickness of the battery cell to be predicted before formation is controlled within 0.5mm. For example, the difference between the thickness of the battery cell to be predicted at the initial voltage V0 and the thickness of the battery cell to be predicted before formation can be 0mm or 0.1mm or 0.15mm or 0.2mm or 0.25mm or 0.3mm or 0.35mm or 0.4mm or 0.45mm or 0.5mm.

[0027] Specifically, the standard battery cell is first fully discharged, and then the standard battery cell is allowed to undergo a constant current charging stage and then a constant voltage charging stage before reaching a fully charged state; in order to be able to detect the thickness change of the standard battery cell in real time during the charging process, a thickness testing fixture is designed. The thickness testing fixture includes two plywood, and the two plywood are respectively arranged on both sides of the thickness direction of the standard battery cell. A displacement sensor is provided on each plywood. Since the area where the standard battery cell bulges is mainly in the middle area, the test ends of the displacement sensor are all facing the middle area of the standard battery cell, and the displacement sensor transmits the tested size information to the processor. After processing by the processor, the mapping relationship between time and thickness size can be obtained. Since constructing a mapping relationship between time and working voltage during the charging process of the standard battery cell is an existing known means, the mapping relationship between thickness size and working voltage can be fitted and constructed.

[0028] Thus, in step S3, to ensure that the difference between the thickness of the battery cell to be predicted when the initial voltage is V0 and the thickness of the battery cell to be predicted before formation is within 0.5mm, the initial voltage V0 can be confirmed by constructing a mapping relationship between thickness dimension and operating voltage. For example, the thickness of the battery cell to be predicted when the initial voltage is V0 is designed to be B0+0.4mm, where B0 is the thickness of the battery cell to be predicted before formation. Then, based on the constructed mapping relationship between thickness dimension and operating voltage and B0+0.4mm, the voltage V can be obtained. As long as the initial voltage V0 is less than or equal to the voltage V, it can be sufficient. For example, if B0 is 35mm, then as long as the thickness of the battery cell to be predicted when the initial voltage is V0 is less than or equal to 35.5mm, it can be sufficient.

[0029] Preferably, since the inventors have found that generally formed battery cells have almost no bulges, in order to simplify the test steps and speed up the test, the battery cell to be predicted can be designed to be a formed battery cell of the same type as the standard battery cell.

[0030] In some embodiments, to ensure that the difference between the thickness of the battery cell to be predicted when the initial voltage V0 is V0 and the thickness of the battery cell to be predicted before formation is within 0.5 mm, the initial voltage V0 of the battery cell to be predicted is not too large, that is, the state of charge value corresponding to the initial voltage V0 of the battery cell to be predicted is not too large. Therefore, based on the mapping relationship between thickness dimension and operating voltage constructed above, the inventors found that it is sufficient to design the first state of charge value to be less than or equal to 50%. In addition, to ensure that two different fitting equations can be fitted, it is necessary to design the difference between the first state of charge value and the fourth state of charge value to be much larger than the difference between the first state of charge value and the second state of charge value, and larger than the difference between the second state of charge value and the third state of charge value. For example, the difference between the first state of charge value and the fourth state of charge value is 10%, while the difference between the first state of charge value and the second state of charge value is 1%. Therefore, the inventors designed the first state of charge value to be greater than or equal to 11%.

[0031] Specifically, the first state of charge value can be 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 134%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42% SOC, 43%, 44%, 45%, 46%, 47%, 48%, 49% or 50%.

[0032] Furthermore, based on the designed value range of the first state of charge value being between 11% and 50%, and based on ensuring that two different fitting equations can be fitted, the value range of the fourth state of charge value is designed to be between 5% and 30%.

[0033] Specifically, the first state of charge value may be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%.

[0034] Furthermore, when fitting the equation, the smaller the data difference is, the smaller the data coverage range of the fitted linear equation is, the smaller the prediction range is, the higher the degree of fitting is, and the higher the prediction accuracy is; the larger the data difference is, the larger the data coverage range of the fitted linear equation is, the larger the prediction range is, the lower the degree of fitting is, and the lower the prediction accuracy is. Therefore, the difference range of the second state of charge value and the first state of charge value, the difference range of the third state of charge value and the second state of charge value, the difference range of the fifth state of charge value and the fourth state of charge value, and the difference range of the sixth state of charge value and the fifth state of charge value are designed to be within an appropriate range, taking into account the prediction range and prediction accuracy of the linear equation, that is, the difference range of the second state of charge value and the first state of charge value is between 1% and 5%; the difference range of the third state of charge value and the second state of charge value is between 1% and 5%; the difference range of the fifth state of charge value and the fourth state of charge value is between 1% and 5%; and the difference range of the sixth state of charge value and the fifth state of charge value is between 1% and 5%.

[0035] Specifically, the difference between the second state of charge value and the first state of charge value may be 1%, 2%, 3%, 4% or 5%; the difference between the third state of charge value and the second state of charge value may be 1%, 2%, 3%, 4% or 5%; the difference between the fifth state of charge value and the fourth state of charge value may be 1%, 2%, 3%, 4% or 5%; the difference between the sixth state of charge value and the fifth state of charge value may be 1%, 2%, 3%, 4% or 5%.

[0036] Furthermore, the difference between the second state of charge value and the first state of charge value, and the difference between the third state of charge value and the second state of charge value may be equal or unequal; the difference between the fifth state of charge value and the fourth state of charge value, and the difference between the sixth state of charge value and the fifth state of charge value may be equal or unequal; in order to further improve the degree of fitting, the difference between the second state of charge value and the first state of charge value is designed to be equal to the difference between the third state of charge value and the second state of charge value, and the difference between the fifth state of charge value and the fourth state of charge value is equal to the difference between the sixth state of charge value and the fifth state of charge value.

[0037] For example, when the difference between the second state of charge value and the first state of charge value is 1%, the difference between the third state of charge value and the second state of charge value is also 1%; when the difference between the fifth state of charge value and the fourth state of charge value is 2%, the difference between the sixth state of charge value and the fifth state of charge value is also 2%.

[0038] It should be noted that in order to ensure that the two fitting equations are fitted under the same conditions, the difference between the second state of charge value and the first state of charge value, the difference between the third state of charge value and the second state of charge value, the difference between the fifth state of charge value and the fourth state of charge value, and the difference between the sixth state of charge value and the fifth state of charge value are all designed to be equal.

[0039] For example, the difference between the second SOC value and the first SOC value, the difference between the third SOC value and the second SOC value, the difference between the fifth SOC value and the fourth SOC value, and the difference between the sixth SOC value and the fifth SOC value are all 1%.

[0040] Furthermore, in order to ensure that the two fitting equations y1=a1x1+b1 and y2=a2x2+b2 are fitted within the linear or sublinear range of the degradation trajectory of the standard battery cell, when the standard battery cell is a lithium iron phosphate battery, with reference to the static OCV-SOC curve of the lithium iron phosphate battery, the value ranges of the first state of charge value and the fourth state of charge value are designed to be between 0% and 20%, or the value ranges of the first state of charge value and the fourth state of charge value are designed to be between 20% and 50%.

[0041] Preferably, since the battery cell to be predicted is a formed battery cell of the same type as the standard battery cell, and the inventors have found that the state of charge corresponding to the residual capacity of a generally formed battery cell is generally around 30%, the first state of charge value and the fourth state of charge value are designed to have a value range between 0% and 20%.

[0042] Specifically, regarding the design of the first to sixth state of charge values, it should be noted that since the standard battery cells are selected after full charge and discharge, that is, the static OCV-SOC curve of the standard battery cells is known, and the discharge curve of the standard battery cells with respect to the state of charge and the operating voltage is also known. Therefore, before conducting a capacity test, the operating voltage V1 at the time of the first discharge stop and the operating voltage V2 at the time of the second discharge stop in the discharge process of the battery cell to be predicted can be designed based on the discharge curve of the standard battery cells with respect to the state of charge and the operating voltage. Then, based on the discharge curve of the standard battery cells with respect to the state of charge and the operating voltage, the second state of charge value corresponding to the discharge of the standard battery cell to the operating voltage V1 and the fifth state of charge value corresponding to the discharge of the standard battery cell to the operating voltage V2 can be determined. Then, the first state of charge value, the third state of charge value, the fourth state of charge value and the sixth state of charge value can be determined using the second state of charge value and the fifth state of charge value as intermediate values, respectively.

[0043] Specifically in this embodiment, the standard battery cell and the battery cell to be predicted are both 88.3Ah lithium iron phosphate batteries. The operating voltage V1 of the battery cell to be predicted when the first discharge stops during the discharge process is designed to be 3.108V. According to the discharge curve of the standard battery cell regarding the state of charge and the operating voltage, the second state of charge value corresponding to the standard battery cell being discharged to the operating voltage V1 is determined to be 10%. In this way, the first state of charge value can be determined to be 11%, and the third state of charge value can be determined to be 9%. The operating voltage V2 of the battery cell to be predicted when the second discharge stops during the discharge process is designed to be the discharge cut-off voltage, that is, V2 is 2.5V. According to the discharge curve of the standard battery cell regarding the state of charge and the operating voltage, the second state of charge value corresponding to the standard battery cell being discharged to the operating voltage V1 is determined to be 10%. In this way, the first state of charge value can be determined to be 11%, and the third state of charge value can be determined to be 9%. The discharge curve of the state of charge and the operating voltage is used to determine that the fifth state of charge value corresponding to the standard battery cell being discharged to the operating voltage V1 is 0%. In this way, the fourth state of charge value can be determined to be 1%, and the sixth state of charge value can be determined to be -1%. Here, the sixth state of charge value of -1% can be understood as, after the battery cell to be predicted is discharged to the discharge cut-off voltage and after the static stage is completed, it continues to discharge 1% SOC at a fixed rate constant current, that is, let the battery cell to be predicted be over-discharged. It should be noted here that when the battery cell to be predicted is over-discharged, the static voltage measured after the over-discharge of the battery cell to be predicted and the static stage is completed is required to be less than the over-discharge protection voltage of the standard battery cell.

[0044] After completing the above-mentioned design of the first state of charge value, the third state of charge value, the fourth state of charge value and the sixth state of charge value, the battery capacity test is started, namely: S1: multiple standard battery cells in a fully charged state are discharged at a constant current of 1C to 11% SOC, and after standing for 30 minutes, the static voltage is recorded; the standard battery cells are continuously discharged at a constant current of 1C to 10% SOC, and after standing for 30 minutes, the static voltage is recorded; the standard battery cells are continuously discharged at a constant current of 1C to 9% SOC, at which time the average working voltage V1 of the multiple standard battery cells at the end of discharge is 3.108V, and after standing for 30 minutes, the static voltage is recorded; the standard battery cells are continuously discharged at a constant current of 1C to 1% SOC, and after standing for 30 minutes, the static voltage is recorded; the standard battery cells are continuously discharged at a constant current of 1C to 0% SOC, and after standing for 30 minutes, the static voltage is recorded; the standard battery cells are continuously discharged at a constant current of 1C to 1% SOC, and after standing for 30 minutes, the static voltage is recorded; The static voltages recorded after the above-mentioned multiple standard battery cells are discharged to 11% SOC and left to stand for 30 minutes are averaged to obtain a first static voltage, which is 3.219 V; the static voltages recorded after the above-mentioned multiple standard battery cells are discharged to 10% SOC and left to stand for 30 minutes are averaged to obtain a second static voltage, which is 3.212 V; the static voltages recorded after the above-mentioned multiple standard battery cells are discharged to 9% SOC and left to stand for 30 minutes are averaged to obtain a third static voltage, which is 3.208 V; the static voltages recorded after the above-mentioned multiple standard battery cells are discharged to 1% SOC and left to stand for 30 minutes are averaged to obtain a fourth static voltage, which is 3.0778 V; the static voltages recorded after the above-mentioned multiple standard battery cells are discharged to 0% SOC and left to stand for 30 minutes are averaged to obtain a fifth static voltage, which is 3.008 V; the static voltages recorded after the above-mentioned multiple standard battery cells are over-discharged by 1% The sixth static voltage is obtained by averaging the static voltages recorded after SOC and standing for 30 minutes. The sixth static voltage is 2.998V.

[0045] Then proceed to step S2, see Figure 1 and Figure 2 , with the static voltage as the abscissa and the state of charge value as the ordinate, a linear fit is performed on the first state of charge value, the second state of charge value, the third state of charge value, the first static voltage, the second static voltage, and the third static voltage, obtaining a first fitting equation y=1.8634x-5.8872; with the static voltage as the abscissa and the state of charge value as the ordinate, a linear fit is performed on the fourth state of charge value, the fifth state of charge value, the sixth state of charge value, the fourth static voltage, the fifth static voltage, and the sixth static voltage, obtaining a second fitting equation y=0.1251x-0.375.

[0046] Then, step S3 is performed to select a battery cell that is of the same type as the standard battery cell and has been formed as the battery cell to be predicted. At this time, the battery cell to be predicted has power.

[0047] Then, step S4 is performed, wherein the battery cell to be predicted is discharged at a constant current of 1C. When the battery cell to be predicted is discharged to an operating voltage of 3.108V, the discharge is stopped. The battery cell to be predicted is controlled to stand for 30 minutes, and the voltage V3 at this time is recorded as 3.2167V.

[0048] Then, step S5 is performed to continue discharging the battery cell to be predicted at a constant current of 1C. When the battery cell to be predicted is discharged to a discharge cut-off voltage of 2.5V, the discharge is stopped, and the discharge capacity C0 during the discharge period is obtained to be 11.72Ah. After the battery cell to be predicted is controlled to stand for 30 minutes, the voltage V4 at this time is recorded as 2.7923V.

[0049] Finally, proceed to step S6, substituting V3 (3.2167 V) into the first fitting equation 1.8634x-5.8872, substituting V4 (2.7923 V) into the second fitting equation y=0.1251x-0.375, and substituting C0 (11.72 Ah) into C=C0÷(y1-y2), thereby obtaining C=11.72÷(10.68%+2.57%)=88.45 Ah.

[0050] From the above, it can be seen that the capacity C of the lithium iron phosphate battery predicted by the above capacity test method is 88.45Ah, which is not much different from the actual capacity of the lithium iron phosphate battery 88.3Ah, and the prediction is accurate.

[0051] It should be noted that, in order to further verify the capacity C of the lithium iron phosphate battery, the first to sixth state of charge values can be adjusted by adjusting V1 and V2, and then steps 1-6 are repeated to obtain the capacity C of the lithium iron phosphate battery.

[0052] It should also be noted that in step S1, the fixed rate used for discharging the standard battery cell ranges from 0.5C to 3C. Specifically, the fixed rate used for discharging the standard battery cell can be 0.5C, 0.65C, 0.75C, 1C, 1.2C, 1.25C, 1.4C, 1.55C, 1.75C, 2C, 2.3C, 2.5C, 2.7C, 2.8C or 3C. In steps S4 and S5, the fixed rate used by the battery cell to be predicted ranges from 0.5C to 3C. Specifically, the fixed rate used by the battery cell to be predicted is 0.5C, 0.7C, 0.9C, 1.1C, 1.3C, 1.4C, 1.5C, 1.6C, 1.7C, 1.8C, 1.9C, 2C, 2.1C, 2.2C, 2.3C, 2.4C, 2.5C, 2.6C, 2.7C, 2.8C, 2.9C or 3C.

[0053] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A battery capacity testing method, characterized in that: The following steps are involved: S1: discharging a fully charged standard battery cell at a fixed rate and constant current to a first state of charge value, controlling the standard battery cell to enter a rest phase, and obtaining a first static voltage of the standard battery cell after the rest phase is completed; Continue to discharge the standard battery cell at a fixed rate constant current to a second state of charge value, and obtain the operating voltage V1 of the standard battery cell at the end of discharge; control the standard battery cell to enter a rest phase, and obtain a second static voltage of the standard battery cell after the rest phase is completed; Continue to discharge the standard battery cell at a fixed rate and constant current to a third state of charge value, control the standard battery cell to enter a rest phase, and obtain a third static voltage of the standard battery cell after the rest phase is completed; Continue discharging the standard battery cell at a fixed rate and constant current to a fourth state of charge value, control the standard battery cell to enter a rest phase, and obtain a fourth static voltage of the standard battery cell after the rest phase is completed; Continue to discharge the standard battery cell at a fixed rate constant current to a fifth state of charge value, and obtain the operating voltage V2 of the standard battery cell at the end of discharge; control the standard battery cell to enter a rest phase, and obtain the fifth static voltage of the standard battery cell after the rest phase is completed; Continue discharging the standard battery cell at a fixed rate and constant current to a sixth state of charge value, control the standard battery cell to enter a rest phase, and obtain a sixth static voltage of the standard battery cell after the rest phase is completed; S2: With the static voltage as the abscissa and the state of charge value as the ordinate, a linear fit is performed on the first state of charge value, the second state of charge value, the third state of charge value, the first static voltage, the second static voltage, and the third static voltage to obtain a first fitting equation y1=a1x1+b1; with the static voltage as the abscissa and the state of charge value as the ordinate, a linear fit is performed on the fourth state of charge value, the fifth state of charge value, the sixth state of charge value, the fourth static voltage, the fifth static voltage, and the sixth static voltage to obtain a second fitting equation y2=a2x2+b2; S3: Acquire a battery cell to be predicted that is of the same type as the standard battery cell, and make the battery cell to be predicted have an initial voltage V0, where V0>V1; S4: discharging the battery cell to be predicted at a fixed rate and constant current. When the battery cell to be predicted is discharged to the operating voltage V1, discharging is stopped and the battery cell to be predicted is controlled to enter a rest phase. The voltage of the battery cell to be predicted after the rest phase is obtained as V3. S5: Continue to discharge the battery cell to be predicted at a fixed rate and constant current. When the battery cell to be predicted is discharged to the operating voltage V2, stop discharging and obtain the discharge capacity C0 during the discharge period; control the battery cell to be predicted to enter a rest phase, and obtain the voltage of the battery cell to be predicted after the rest phase as V4; S6: According to steps S2-S5 and the formula C=C0÷(y1-y2), C=C0÷[(a1V3+b1)-(a2V4+b2)] is obtained, wherein C is the capacity of the battery cell to be predicted after being fully charged and discharged to the discharge cut-off voltage.

2. The battery capacity testing method according to claim 1, wherein: In step S3 , the battery cell to be predicted is a formed battery cell of the same type as the standard battery cell.

3. The battery capacity testing method according to claim 1, wherein: In step S1, the first state of charge value ranges from 11% to 50%; the difference between the second state of charge value and the first state of charge value ranges from 1% to 5%; and the difference between the third state of charge value and the second state of charge value ranges from 1% to 5%.

4. The battery capacity testing method according to claim 3, characterized in that: In step S1, the fourth state of charge value ranges from 5% to 30%; the difference between the fifth state of charge value and the fourth state of charge value ranges from 1% to 5%; and the difference between the sixth state of charge value and the fifth state of charge value ranges from 1% to 5%.

5. The battery capacity testing method according to claim 4, characterized in that: In step S1, the first state of charge value and the fourth state of charge value both have a value range of 0% to 20%; or, the first state of charge value and the fourth state of charge value both have a value range of 20% to 50%.

6. The battery capacity testing method according to claim 4, characterized in that: In step S1, a difference between the second state of charge value and the first state of charge value, a difference between the third state of charge value and the second state of charge value, a difference between the fifth state of charge value and the fourth state of charge value, and a difference between the sixth state of charge value and the fifth state of charge value are all equal.

7. The battery capacity testing method according to claim 4 or 6, characterized in that: In step S1 , the fifth state of charge value is 0%, and the operating voltage V2 is the discharge cut-off voltage of the standard battery cell.

8. The battery capacity testing method according to claim 7, characterized in that: In step S1 , the operating voltage of the standard battery cell when the standard battery cell is discharged at a constant current to a sixth state of charge value is lower than the over-discharge protection voltage of the standard battery cell.

9. The battery capacity testing method according to claim 8, characterized in that: In step S2, the first fitting equation is y1=1.8634x1-5.8872; the second fitting equation is y2=0.1251x2-0.

375.

10. The battery capacity testing method according to claim 1, wherein: In step S3 , the difference between the thickness of the battery cell to be predicted at the initial voltage V0 and the thickness of the battery cell to be predicted before formation is controlled to be within 0.5 mm.

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