Test method and system for prolonging cycle life of lithium ion battery

Abstract

The invention discloses a test method and system for prolonging the cycle life of a lithium ion battery, belongs to the technical field of lithium ion batteries, and solves the problems of how to determine the charge-discharge upper and lower limit range of a to-be-tested battery and how to prolong the cycle life of the to-be-tested battery. The method comprises the following steps: S1, determining a proper SOC interval (X, Y); s2, charging and discharging the to-be-detected battery for multiple circles, fixing the volume of the to-be-detected battery, and determining C0 and V0; s3, determining a test scheme of SOC interval circulation according to the type of the to-be-tested battery; according to different corresponding relations of SOC and OCV of the ternary battery and the lithium iron battery, an SOC interval cycle test scheme for different battery types is provided from a test perspective, the SOC interval range of the ternary battery and the lithium iron battery is accurately controlled, the test effect of prolonging the cycle life of the battery is achieved, the discharge capacity can be influenced to a relatively small extent, and the test efficiency is improved. And the cycle life of the battery is prolonged, so that an equipment user can keep good experience of using the equipment for a long time in a relatively long time, and the battery replacement cost of the equipment user is saved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and relates to a test method and system for extending the cycle life of lithium-ion batteries. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, high power density, good safety performance, fast charge and discharge, long cycle life, pollution-free and no memory effect, etc., and are widely used in portable devices, aerospace, urban rail transit (such as power supplies required for electric vehicles and hybrid vehicles), etc. With the increasing global environmental pollution and energy crisis, electric vehicles gradually replace fuel vehicles because they use lithium-ion batteries as the power supply system, which is safe and pollution-free. Power lithium-ion batteries are the heart of electric vehicles, and their life is a key factor affecting the use of electric vehicles.

[0003] The life of a lithium-ion battery is not calculated according to the traditional number of charging times, but based on the charge and discharge cycle of the battery. This cycle refers to the process of discharging the battery from a fully charged state to depletion, and then charging it from the depleted state to full charge. Whenever the battery completes such a complete charge and discharge cycle, its life will be reduced by one time. The life of a lithium-ion battery is usually expressed in terms of the number of cycles. For example, a battery may be rated at the design stage to be able to complete 500 charge and discharge cycles. This means that after the battery completes 500 processes from full charge to depletion and then from depletion to full charge, its capacity and performance may begin to decline significantly. Therefore, in order to protect the life of the lithium-ion battery, frequent full charge and full discharge should be avoided as much as possible. Of course, in practice, only a partial SOC range is often used, and the full charge-full discharge process is rarely experienced.

[0004] The prior art, such as the invention patent with the application publication number CN112599876A, discloses a regulation method for extending the service life of a lithium-ion battery pack. By calibrating the capacity of the battery pack to be tested, determining the charging cut-off voltage according to the charging capacity data of the capacity calibration, and finally performing a charge and discharge cycle life test according to the determined charging cut-off voltage and discharge cut-off voltage, this method does not require the development of the battery interior, and only by regulating the voltage parameters during the use of a mature product, the service life of the product can be extended, greatly reducing the R & D cost. However, the SOC range involved in this technology is 0-80% DOD. Compared with full charge and full discharge, 20% of the capacity is lost each time of discharge, and 1 / 5 of the cruising range will be lost, and the life is only extended by about 3%. On the basis of extending the life, the capacity should not drop too much compared with full charge and full discharge. Thus, it can be seen that the prior art still needs to further optimize how to determine the upper and lower limits of the charge and discharge voltage range and the SOC range, and the test scheme for the SOC range cycle. Summary of the Invention

[0005] The technical problem to be solved by the present invention is how to determine the charge and discharge upper and lower limit ranges of the battery to be tested and extend the cycle life of the battery to be tested.

[0006] The present invention solves the above technical problem through the following technical solutions:

[0007] A test method for extending the cycle life of a lithium-ion battery, comprising the following steps:

[0008] S1. Determine a suitable SOC interval (X, Y); where X represents the lower limit of the interval cycle and Y represents the upper limit of the interval cycle;

[0009] S2. Charge and discharge the battery to be tested for multiple cycles, fix the volume of the battery to be tested, and determine the fixed volume capacity C 0 and the charging cut-off voltage V 0 ;

[0010] S3. Determine the test scheme for the SOC interval cycle according to the type of the battery to be tested;

[0011] S4. Repeat steps S2 to S3 until the lithium battery is taken out of the cabinet.

[0012] In view of the different corresponding relationships between SOC and OCV of ternary batteries and lithium iron phosphate batteries, the present invention provides a SOC interval cycle test scheme for different battery types from the test perspective, accurately controls the SOC interval range of ternary batteries and lithium iron phosphate batteries, has the test effect of extending the battery cycle life, can affect the discharge capacity to a small extent, extends the cycle life of the battery, enables device users to maintain a good experience of using the device for a long time, and saves the battery replacement cost of device users.

[0013] Further, the S2 includes:

[0014] S21. Discharge the battery to be tested at a constant current of I 2 to the lower limit voltage and then let it stand;

[0015] S22. Charge the battery to be tested at a constant current and constant voltage of I 3 to the upper limit voltage and then let it stand, and then charge it at a constant voltage until the current is 0.05C and then let it stand;

[0016] S23. Repeat S21 to S22, record the last discharge capacity as C 0 , and the voltage corresponding to Y% SOC of the last charge capacity is V 0 .

[0017] Further, the standing time in S2 is 30 min.

[0018] Further, the upper limit voltage is the highest voltage within the battery's operating range, the lower limit voltage is the lowest voltage within the battery's operating range, the voltage corresponding to Y% SOC is the charge cut-off voltage, and the voltage corresponding to X% SOC is the discharge cut-off voltage.

[0019] Further, S3 includes:

[0020] S31. When the battery under test is a ternary battery, perform the following steps:

[0021] S311. Discharge the battery under test at a constant current of I 2 until the lower limit voltage is reached, and then let it stand.

[0022] S312. Charge the battery under test at a constant current and constant voltage of I 3 until the upper limit voltage is reached, then let it stand, and then continue to charge at a constant voltage until the current is 0.05C, and then let it stand.

[0023] S313. Discharge the battery under test at a constant current of I 2 until the X% SOC state is reached, and stop discharging after discharging (100 - X)% SOC of the battery's charge, and then let it stand.

[0024] S314. Charge the battery under test at a constant current of I 3 until the voltage V 0 is reached, then let it stand, and then continue to charge at a constant voltage until the current is 0.05C, and then let it stand. At this time, the battery is in the Y% SOC state.

[0025] S315. Discharge the battery under test at a constant current of I 2 until the X% SOC state is reached, and stop discharging after discharging (Y - X)% SOC of the battery's charge, and then let it stand.

[0026] S316. Repeat S314 - S315 until the cut-off condition is met.

[0027] Further, S3 also includes:

[0028] S32. When the battery under test is a lithium iron phosphate battery, perform the following steps:

[0029] S321. Discharge the battery under test at a constant current of I 2 until the lower limit voltage is reached, and then let it stand.

[0030] S322. Charge the battery under test at a constant current and constant voltage of I 3 until the upper limit voltage is reached, then let it stand, and then continue to charge at a constant voltage until the current is 0.05C, and then let it stand.

[0031] S323. Discharge the battery under test at a constant current of I 2 until the X% SOC state is reached, and stop discharging after discharging (100 - X)% SOC of the battery's charge, and then let it stand.

[0032] S324. Charge the battery under test at a constant current of I 3 until the voltage reaches V 0 and then let it stand. At this time, the battery is in the Y% SOC state, and record the charged capacity as C x ;

[0033] S325. Discharge the battery under test at a constant current of I 2 until the discharged charge reaches Cx, then cut off and let it stand;

[0034] S326. Repeat S324 - S325 until the cut-off condition is met.

[0035] Furthermore, the cut-off condition in S3 is that the battery retention rate is lower than 80%.

[0036] Furthermore, the standing time in S3 is 10 min.

[0037] A test system for extending the cycle life of a lithium-ion battery, comprising:

[0038] An interval definition module for determining a suitable SOC interval (X, Y); where X represents the lower limit of the interval cycle and Y represents the upper limit of the interval cycle;

[0039] A battery constant volume module for charging and discharging the battery under test for multiple cycles, determining the constant volume of the battery under test, and determining the constant volume capacity C 0 and the charging cut-off voltage V 0 ;

[0040] The battery cycle module is used to determine the test scheme for SOC interval cycling for the battery type under test;

[0041] The repeated execution module is used to repeatedly execute the battery constant volume module to the battery cycle module until the lithium battery is taken out of the cabinet.

[0042] Furthermore, the battery constant volume module includes:

[0043] The first stage: Discharge the battery under test at a constant current of I 2 until the lower limit voltage is reached and then let it stand;

[0044] The second stage: Charge the battery under test at a constant current and constant voltage of I 3 until the upper limit voltage is reached and then let it stand, and then charge at a constant voltage until the current is 0.05C and then let it stand;

[0045] The third stage: Repeat the first stage to the second stage, record the last discharge capacity as C 0 , and the voltage corresponding to Y% SOC of the last charge capacity is V 0 .

[0046] The advantages of the present invention are:

[0047] In view of the unique correspondence of the SOC-OCV curve of ternary batteries, according to the OCV value corresponding to a certain SOC, the cut-off voltages for charge and discharge in interval cycling are output. However, the SOC-OCV curve of lithium iron phosphate batteries has a relatively long voltage plateau, and it is relatively inaccurate to use OCV to find the SOC in interval cycling. In the present invention, the voltage corresponding to Y% SOC is first found, and then the capacity of Y% SOC is discharged from full charge. At this time, it is in the state of X% SOC. When charging to the voltage corresponding to Y% SOC, the capacity during this charging process is considered to be the capacity of (Y - X)% SOC, thereby realizing the interval cycling of X% to Y% SOC. The cycling interval test scheme disclosed in the present invention greatly extends the cycle life of the battery on the basis of minimizing the impact on capacity utilization. From the perspective of the cycling trend, the life of lithium iron phosphate batteries increases by nearly 2 times, and the life of ternary batteries increases by nearly 1 time. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a flowchart of a test method for extending the cycle life of lithium-ion batteries according to Embodiment 1 of the present invention;

[0049] Figure 2 is a graph of voltage vs. capacity of a ternary battery according to Embodiment 2 of the present invention;

[0050] Figure 3 is a graph of SOC vs. voltage of a ternary battery according to Embodiment 2 of the present invention;

[0051] Figure 4 is a comparison graph of interval cycling from 1-96% and full charge-discharge cycling of a ternary battery according to Embodiment 2 of the present invention;

[0052] Figure 5 is a graph of voltage vs. capacity of a lithium iron phosphate battery according to Embodiment 3 of the present invention;

[0053] Figure 6 is a graph of SOC vs. voltage of a lithium iron phosphate battery according to Embodiment 3 of the present invention;

[0054] Figure 7 is a comparison graph of interval cycling from 2-98% and full charge-discharge cycling of a lithium iron phosphate battery according to Embodiment 3 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0056] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments:

[0057] Embodiment 1

[0058] As Figure 1 shown, specifically, a test method for extending the cycle life of a lithium-ion battery is disclosed, including the following steps:

[0059] S1. Determine a suitable SOC range (X, Y); where X represents the lower limit of the interval cycle and Y represents the upper limit of the interval cycle. In this embodiment, the SOC range is usually input by the client, and the temperature during the test is 25°C ± 2°C.

[0060] S2. Charge and discharge the battery under test for 4 cycles, fix the volume of the battery under test, and determine the fixed volume capacity C 0 and the charging cut-off voltage V 0 ;

[0061] In this embodiment, S2 includes the following steps:

[0062] S21. Discharge the battery under test at a constant current of I 2 to the lower limit voltage and then let it stand;

[0063] S22. Charge the battery under test at a constant current and constant voltage of I 3 to the upper limit voltage, and then charge it at a constant voltage until the current is 0.05C and then let it stand;

[0064] S23. Repeat S21 - S22 four times, record the last discharge capacity as C 0 , and the voltage corresponding to Y% SOC of the last charge capacity is V 0 .

[0065] In this embodiment, in order to less affect the magnitude of the discharge capacity, the upper limit Y of the interval cycle takes a value between 95% and 99%, and the specific value is comprehensively judged according to each lithium battery system; I 2 represents the first charge and discharge rate, I 3 represents the second charge and discharge rate. In this embodiment, I 2 takes C / 2, I 3 takes C / 3, and the charge and discharge rates include but are not limited to the above values, and the specific values can be determined according to the performance of the lithium battery.

[0066] Furthermore, the standing time in S2 is 30 min.

[0067] Further, the upper limit voltage is the highest voltage within the battery's operating range, the lower limit voltage is the lowest voltage within the battery's operating range, the voltage corresponding to Y% SOC is the charge cut-off voltage, and the voltage corresponding to X% SOC is the discharge cut-off voltage.

[0068] S3. Determine the test scheme for the SOC interval cycle for the battery type to be tested;

[0069] The ternary battery is a lithium battery with nickel, cobalt, and manganese (or aluminum) as the cathode material. The ternary battery has a significant improvement in energy density compared to traditional cobalt acid lithium batteries. The SOC and OCV of the ternary battery are relatively linear, and it can be considered that there is a unique corresponding relationship between the SOC and OCV of the ternary battery; while the cathode material of the lithium iron phosphate battery (LiFePO 4 ) is lithium iron phosphate. Compared with the ternary battery, the lithium iron phosphate battery has a relatively lower energy density, but has higher safety, a longer service life, and lower cost. The relationship between the SOC and OCV of the lithium iron phosphate battery is relatively flat, and there are multiple SOC values corresponding to the same OCV value. Therefore, for different types of lithium battery types, the test scheme for the SOC interval cycle is also different. Specifically, the S3 includes:

[0070] S31. When the battery to be tested is a ternary battery, perform the following steps:

[0071] S311. Discharge the battery to be tested at a constant current of I 2 until the lower limit voltage, and then let it stand;

[0072] S312. Charge the battery to be tested at a constant current and constant voltage of I 3 until the upper limit voltage, then let it stand, and then charge it at a constant voltage until the current is 0.05C and then let it stand;

[0073] S313. Discharge the battery to be tested at a constant current of I 2 until the X% SOC state, and stop discharging after discharging (100 - X)% SOC of the battery and then let it stand;

[0074] S314. Charge the battery to be tested at a constant current of I 3 until V 0 , then let it stand, and then charge it at a constant voltage until the current is 0.05C and then let it stand. At this time, the battery is in the Y% SOC state;

[0075] S315. Discharge the battery to be tested at a constant current of I 2 until the X% SOC state, and stop discharging after discharging (Y - X)% SOC of the battery and then let it stand;

[0076] S316. Repeat S314 - S315 until the cut-off condition is met.

[0077] The S3 also includes:

[0078] S32. When the battery under test is a lithium iron phosphate battery, perform the following steps:

[0079] S321. Discharge the battery under test at a constant current of I 2 until the lower limit voltage is reached, and then let it stand still;

[0080] S322. Charge the battery under test at a constant current and constant voltage of I 3 until the upper limit voltage is reached, then let it stand still, and then charge it at a constant voltage until the current is 0.05C, and then let it stand still;

[0081] S323. Discharge the battery under test at a constant current of I 2 until the X% SOC state is reached, and stop discharging after discharging (100 - X)% SOC of the battery capacity, and then let it stand still;

[0082] S324. Charge the battery under test at a constant current of I 3 until V 0 is reached, and then let it stand still. At this time, the battery is in the Y% SOC state, and record the charged capacity as C x ;

[0083] S325. Discharge the battery under test at a constant current of I 2 until the discharged capacity is C x , and then stop discharging and let it stand still;

[0084] S326. Repeat S324 - S325 until the cut-off condition is met.

[0085] In this embodiment, the cut-off condition is that the battery retention rate is lower than 80%. Specifically, the battery retention rate is the discharge capacity of the battery under test in one charge and discharge cycle at the current cycle stage divided by the average discharge capacity of the battery under test in the first 10 or 5 charge and discharge cycles at the initial stage of discharge.

[0086] Furthermore, the standing time in S3 is 10 min or other durations.

[0087] S4. Repeat steps S2 - S3 until the lithium battery is taken out of the cabinet.

[0088] Embodiment 2

[0089] As Figures 2 - 4 shown, this embodiment takes a ternary battery with an input SOC range of 1 - 96% as an example for illustration. As Figure 3 shown, the SOC - OCV of the ternary battery shows a good linear relationship. At the same charging rate, according to the SOC - OCV curve, the voltage V 0 corresponding to 96% SOC can be found, and the battery under test is charged to V 0 at the same charging rate. As the lithium battery ages, the V 0It is also constantly changing and may be increasing. Therefore, it is necessary to update V every 30 days or within the time required by the customer. 0 , in this embodiment, V 0 represents the voltage corresponding to the state where the battery under test is at 96% SOC. Determine the voltage corresponding to 1% SOC according to the same method above. The voltage corresponding to 1% SOC with the same rate is the voltage corresponding to 1% SOC. It can be cutoff by voltage or by capacity.

[0090] In this embodiment, because the charge rate and discharge rate during the constant volume stage of the battery under test are I3 and I3 respectively at regular intervals; and the charge rate and discharge rate during the cycling stage are I3 and I2 respectively, so the charge rates in the two stages are the same. The voltage corresponding to 96% SOC can be used as the cutoff voltage for the interval cycle, while the discharge rates are different. It is not possible to directly find the voltage corresponding to 1% SOC from the discharge data during constant volume. Therefore, it is more convenient to use capacity cutoff. In this embodiment, the test method for the cycle life of the battery under test, which is a ternary battery, includes the following steps:

[0091] S1’. Determine a suitable SOC interval (1, 96).

[0092] S2’. During the constant volume stage, charge and discharge the battery under test for 4 cycles to fix the volume of the battery under test. S2’ includes the following steps:

[0093] S21’. Discharge the battery under test at a constant current of 50A to the lower limit voltage;

[0094] S22’. Let it stand for 30 minutes;

[0095] S23’. Charge the battery under test at a constant current of 50A to the upper limit voltage, and then switch to constant voltage charging until the current is 0.05C;

[0096] S24’. Let it stand for 30 minutes;

[0097] S25’. Repeat S21’ to S24’ four times. Record the voltage corresponding to 96% SOC of the charging capacity in the last cycle as 4.112V, and the discharge capacity in the last cycle is 150AH.

[0098] S3’. During the cycling stage, S3’ includes the following steps:

[0099] S31’. Discharge the battery under test at a constant current of 75A to the lower limit voltage;

[0100] S32’. Let it stand for 10 minutes;

[0101] S33’. Charge the battery under test at a constant current of 50A to 4.112V, and then switch to constant voltage charging until the current is 7.5A;

[0102] S34’: Stand still for 10 minutes;

[0103] S35’: Discharge the capacity of 142.5 Ah of the battery under test at a constant current of 75 A;

[0104] S36’: Stand still for 10 minutes;

[0105] S37’: Repeat S33’ to S36’ until the required 30-day cycle is reached.

[0106] S4’: Repeat S2’ to S3’ until the battery is taken out of the cabinet. The test curve of the cycle life of the ternary battery is as Figure 4 shown.

[0107] In this embodiment, take C / 3 = 50 A, C / 2 = 75 A, V 0 = 4.112 V, C 0 = 150 AH, 0.05C = 7.5 A, the capacity at 95% SOC is 142.5 Ah, and the cut-off condition for the cycle stage is 30 days of cycle.

[0108] Comparative Example 1

[0109] The ternary batteries of the same batch are subjected to cycle testing using a full charge and full discharge test scheme with the same charge and discharge rate as in Example 2. The test results are as Figure 4 shown.

[0110] Example 3

[0111] As Figures 5 - 7 shown, this embodiment takes a lithium iron phosphate battery with an input SOC range of 2 - 98% as an example for illustration. As Figure 6 shown, the SOC and voltage curves of the lithium iron phosphate battery do not have a good linear relationship; at the same charging rate, the voltage V 0 corresponding to 98% SOC can be found. Then, at the same charging rate, charge to V 0 . Of course, as the battery ages, the V 0 corresponding to 98% SOC is also constantly changing, and it may increase. Therefore, it is necessary to update V 0 every 30 days or within the time required by the customer to represent the state of the battery at 98% SOC. Due to the characteristics of the voltage curve of the lithium iron phosphate battery, it is more accurate to cut off by capacity. If charging to V 0 , discharging to 96% SOC, and then charging to the state of 98% SOC is inaccurate. Therefore, this embodiment adopts a test method of discharging the same amount of capacity as the charged capacity. The test method for the cycle life of the battery under test being a lithium iron phosphate battery includes the following steps:

[0112] S1”: Determine a suitable SOC range (2, 98).

[0113] S2”, the constant volume stage, the battery under test is charged and discharged 4 cycles to determine the constant volume of the battery under test. S2” includes the following steps:

[0114] S21”, discharge the battery under test at a constant current of 40 A to the lower limit voltage;

[0115] S22”, let it stand for 30 minutes;

[0116] S23”, charge the battery under test at a constant current of 40 A to the upper limit voltage, then switch to constant voltage charging until the current is 6 A;

[0117] S24”, let it stand for 30 minutes;

[0118] S25”, repeat S21” to S24” four cycles. Record the voltage corresponding to 98% of the charging capacity in the last cycle as 3.507 V, and the discharging capacity in the last cycle is 120 Ah.

[0119] In this embodiment, the voltage V corresponding to 98% 0 is updated by re-determining the constant volume every 30 days.

[0120] S3”, the cycling stage, S3” includes the following steps:

[0121] S31”, discharge the battery under test at a constant current of 60 A to the lower limit voltage;

[0122] S32”, let it stand for 10 minutes;

[0123] S33”, charge the battery under test at a constant current of 40 A to 3.507 V, then switch to constant voltage charging until the current is 6 A;

[0124] S34”, let it stand for 10 minutes;

[0125] S35”, discharge 117.6 Ah of the battery under test at a constant current of 60 A. At this time, it is considered to be in the 2% SOC state;

[0126] S36”, let it stand for 10 minutes;

[0127] S37”, charge the battery under test at a constant current of 40 A to 3.507 V. At this time, it is considered to be in the 98% SOC state, and record the charging capacity C x as 113.74 Ah;

[0128] In this embodiment, the charging capacity determines the discharging capacity, and the discharging capacity each time is different, showing a downward trend as a whole.

[0129] S38”, let it stand for 10 minutes;

[0130] S39”, discharge 113.74 Ah of the battery under test at a constant current of 60 A;

[0131] "S310", leave it standing for 10 minutes;

[0132] "S311", loop "S37" to "S310" until the required 30-day cycle is reached.

[0133] "S4", repeat "S2" to "S3" until the battery is taken out of the cabinet. The test curve of the cycle life of the lithium iron phosphate battery is as Figure 7 shown.

[0134] In this embodiment, take C / 3 = 40A, C / 2 = 60A, V 0 = 3.507V, C 0 = 120Ah, 0.05C = 6A, 98% of C 0 has a capacity of 117.6Ah, the charged capacity C x is 113.74Ah, and the cut-off condition for the cycle stage is 30 days of cycling.

[0135] Comparative Example 2

[0136] Lithium iron phosphate batteries of the same batch are subjected to a cycle test using a full charge and full discharge test scheme with the same charge and discharge rate as in Example 3. The test results are as Figure 7 shown.

[0137] Example 4

[0138] The present invention also discloses a test system for extending the cycle life of a lithium-ion battery, including an interval definition module, a battery constant capacity module, a battery cycle module, and a repeated execution module;

[0139] The interval definition module is used to determine a suitable SOC interval (X, Y); where X represents the lower limit of the interval cycle and Y represents the upper limit of the interval cycle. In this embodiment, the SOC interval is usually input by the client, and the temperature during the test is 25°C ± 2°C.

[0140] The battery constant capacity module is used to charge and discharge the battery under test 4 times to determine the constant capacity C 0 and the charging cut-off voltage V 0 , specifically:

[0141] In the first stage, discharge the battery under test at a constant current of I 2 to the lower limit voltage and then leave it standing;

[0142] In the second stage, charge the battery under test at a constant current and constant voltage of I 3 to the upper limit voltage, and then charge it at a constant voltage until the current is 0.05C and then leave it standing;

[0143] In the third stage, repeat the first stage to the second stage 4 times, and record the last discharge capacity as C 0, the voltage corresponding to Y% SOC of the last charge capacity is V 0 .

[0144] In this embodiment, in order to have a relatively small impact on the discharge capacity, the upper limit Y of the interval cycle takes a value between 95% and 99%, and the specific value is determined comprehensively according to each lithium battery system; I 2 represents the first charge-discharge rate, and I 3 represents the second charge-discharge rate. In this embodiment, I 2 takes C / 2, and I 3 takes C / 3. The charge-discharge rate includes but is not limited to the above values, and the specific value can be determined according to the performance of the lithium battery.

[0145] Furthermore, the standing time in the battery constant volume module is 30 min.

[0146] Furthermore, the upper limit voltage is the highest voltage within the battery operating range, the lower limit voltage is the lowest voltage within the battery operating range, the voltage corresponding to Y% SOC is the charge cut-off voltage, and the voltage corresponding to X% SOC is the discharge cut-off voltage.

[0147] The battery cycle module is used to determine the test scheme for the SOC interval cycle for the battery type to be tested. The battery cycle module includes a ternary battery cycle unit and a lithium iron phosphate battery cycle unit;

[0148] The ternary battery cycle unit is specifically:

[0149] When the battery to be tested is a ternary battery, it includes:

[0150] The first stage is to discharge the battery to be tested at a constant current of I 2 until the lower limit voltage and then stand still;

[0151] The second stage is to charge the battery to be tested at a constant current and constant voltage of I 3 until the upper limit voltage and then stand still, and then charge at a constant voltage until the current is 0.05C and then stand still;

[0152] The third stage is to discharge the battery to be tested at a constant current of I 2 until the X% SOC state, and stand still after discharging (100 - X)% SOC of the electricity;

[0153] The fourth stage is to charge the battery to be tested at a constant current of I 3 until V 0 and then stand still, and then charge at a constant voltage until the current is 0.05C and then stand still. At this time, the battery is in the Y% SOC state;

[0154] The fifth stage is to charge the battery to be tested at a constant current of I 2The current discharges the battery under test at a constant current until it reaches the X% SOC state, stops discharging after discharging (Y - X)% SOC of electricity, and then stands still.

[0155] In the sixth stage, the fourth stage to the fifth stage are cycled until the cut-off condition is met.

[0156] When the battery under test is a lithium iron phosphate battery, it includes:

[0157] In the first stage, the battery under test is discharged at a constant current of I 2 until the lower limit voltage is reached, and then it stands still.

[0158] In the second stage, the battery under test is charged at a constant current and constant voltage of I 3 until the upper limit voltage is reached, then it stands still, and then it is charged at a constant voltage until the current is 0.05C, and then it stands still.

[0159] In the third stage, the battery under test is discharged at a constant current of I 2 until it reaches the X% SOC state, stops discharging after discharging (100 - X)% SOC of electricity, and then stands still.

[0160] In the fourth stage, the battery under test is charged at a constant current of I 3 until it reaches V 0 and then stands still. At this time, the battery is in the Y% SOC state, and the charged capacity is recorded as C x ;

[0161] In the fifth stage, the battery under test is discharged at a constant current of I 2 until the electricity of Cx is discharged, then it stops and stands still.

[0162] In the sixth stage, the fourth stage to the fifth stage are cycled until the cut-off condition is met.

[0163] In this embodiment, the cut-off condition is that the battery retention rate is lower than 80%. Specifically, the battery retention rate is the discharge capacity of the battery under test in one charge and discharge cycle in the current cycle stage divided by the average discharge capacity of the battery under test in the first 10 or 5 charge and discharge cycles at the beginning of discharge.

[0164] Further, the standing time in the battery cycling module is 10 min or other durations.

[0165] The repeated execution module is used to repeatedly execute the battery constant volume module to the battery cycling module until the lithium battery is taken out of the cabinet.

[0166] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A test method for extending the cycle life of a lithium-ion battery, characterized in that: The following steps are involved: S1. Determine a suitable SOC interval (X, Y); wherein X represents the lower limit of the interval cycle, and Y represents the upper limit of the interval cycle; S2, charge and discharge the battery to be tested for multiple cycles, set the capacity of the battery to be tested, and determine the fixed capacity C0 and the charging cut-off voltage V0; S3, determining a test plan for SOC interval cycle according to the type of battery to be tested; S4. Repeat steps S2 to S3 until the lithium battery is removed from the cabinet.

2. A test method for extending the cycle life of a lithium-ion battery according to claim 1, characterized in that: The S2 includes: S21, discharge the battery to be tested to the lower limit voltage with constant current I2 and then let it stand; S22, charging the battery to be tested to the upper limit voltage with constant current and constant voltage of I3, and then letting it stand, and then charging at constant voltage until the current reaches 0.05C, and then letting it stand; S23, repeating S21 to S22, recording the last discharge capacity as C0, and the voltage corresponding to the Y% SOC of the last charge capacity as V0.

3. A test method for extending the cycle life of a lithium-ion battery according to claim 2, characterized in that: The standing time in S2 is 30 min.

4. A test method for extending the cycle life of a lithium-ion battery according to claim 2, characterized in that: The upper limit voltage is the highest voltage within the battery operating range, the lower limit voltage is the lowest voltage within the battery operating range, the voltage corresponding to Y% SOC is the charge cut-off voltage, and the voltage corresponding to X% SOC is the discharge cut-off voltage.

5. A testing method for extending the cycle life of a lithium-ion battery according to claim 1, characterized in that: The S3 includes: S31. When the battery to be tested is a ternary battery, perform the following steps: S311, discharging the battery to be tested to the lower limit voltage with a constant current of I2 and then leaving it to stand; S312, charging the battery to be tested to the upper limit voltage with I3 constant current and constant voltage, and then letting it stand, and then charging at constant voltage until the current reaches 0.05C, and then letting it stand; S313, discharge the battery to be tested to X% SOC state with I2 constant current, and let it stand after the amount of electricity discharged reaches (100-X)% SOC; S314, charging the battery to be tested to V0 with a constant current of I3 and then letting it stand, and then charging it at a constant voltage until the current reaches 0.05C and then letting it stand. At this time, the battery is in a Y% SOC state; S315, discharging the battery to be tested to a state of X% SOC with a constant current of I2, and leaving it to stand until (YX)% SOC is discharged; S316. Loop S314 to S315 until the end condition is met.

6. A test method for extending the cycle life of a lithium-ion battery according to claim 5, characterized in that: The S3 further includes: S32. When the battery to be tested is a lithium iron battery, perform the following steps: S321, discharging the battery to be tested to the lower limit voltage with a constant current of I2 and then leaving it to stand; S322, charging the battery to be tested to the upper limit voltage with I3 constant current and constant voltage, and then letting it stand, and then charging it at constant voltage until the current reaches 0.05C, and then letting it stand; S323, discharge the battery to be tested to X% SOC state with I2 constant current, and let it stand after the battery is discharged until (100-X)% SOC is reached; S324, charge the battery to V0 with constant current I3 and then leave it to stand. At this time, the battery is in Y% SOC state, and the charged capacity is recorded as C x ; S325, discharging the battery to be tested with a constant current of I2 until the amount of electricity Cx is discharged, then cutting off and leaving it to stand; S326. Loop S324-S325 until the cutoff condition is met.

7. A test method for extending the cycle life of a lithium-ion battery according to claim 6, characterized in that: The cut-off condition in S3 is that the battery retention rate is lower than 80%.

8. A test method for extending the cycle life of a lithium-ion battery according to claim 6, characterized in that: The standing time in S3 is 10 min.

9. A test system for extending the cycle life of a lithium-ion battery, characterized in that: include: An interval definition module is used to determine a suitable SOC interval (X, Y); wherein X represents the lower limit of the interval cycle and Y represents the upper limit of the interval cycle; The battery capacity determination module is used to perform multiple cycles of charge and discharge on the battery to be tested, determine the capacity C0 and the charging cut-off voltage V0 of the battery to be tested; The battery cycle module is used to determine the test scheme of SOC interval cycle according to the battery type to be tested; The repeated execution module is used to repeatedly execute the battery capacity determination module to the battery circulation module until the lithium battery is removed from the cabinet.

10. A testing system for extending the cycle life of a lithium-ion battery according to claim 9, characterized in that: The battery capacity constant module comprises: In the first stage, the battery to be tested is discharged to the lower limit voltage with constant current I2 and then left to stand; In the second stage, the battery to be tested is charged to the upper limit voltage with I3 constant current and constant voltage, and then left to stand, and then charged at constant voltage until the current reaches 0.05C, and then left to stand; In the third stage, the first stage to the second stage are repeatedly executed, and the last discharge capacity is recorded as C0, and the voltage corresponding to the Y% SOC of the last charge capacity is recorded as V0.

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