Method for improving cyclic rising of battery, and lithium ion battery

Abstract

A method for improving cyclic rising of a battery, and a lithium ion battery. The method comprises: using a preset charging current to carry out constant-current constant-voltage charging on a battery to be tested until the voltage of said battery reaches a rated voltage, and the current of said battery reaches a target cutoff current (S110); and sequentially carrying out constant-current discharging on said battery twice, wherein a method for carrying out constant-current discharging on said battery comprises: standing said battery for a first preset duration; and when standing is finished, carrying out constant-current discharging on said battery until the voltage of said battery reaches a preset cutoff voltage (S120).

Description

Method for improving battery cycle ramp-up and lithium-ion battery Technical Field

[0001] The embodiments of the present application relate to the technical field of lithium-ion batteries, for example, to a method for improving battery cycle ramp-up and a lithium-ion battery. Background Art

[0002] During the research and development of lithium-ion battery materials, these materials must be fabricated into battery cells and subjected to performance tests such as capacity, direct current resistance (DCR), storage, gas production, and cycling. During cycling tests, cells made with certain materials can experience a gradual increase in capacity initially, a phenomenon known as cycling ramp-up.

[0003] When designing soft-pack batteries, in order to reserve lithium insertion sites for the positive electrode, the negative electrode is generally overdesigned to avoid lithium deposition on the negative electrode and the formation of lithium dendrites, which pierce the diaphragm and cause a short circuit in the battery, creating a safety hazard. Among them, the overdesigned area of ​​the negative electrode compared to the positive electrode is called the Overhang area. During the high-temperature aging test of the battery, lithium ions diffuse evenly around the negative electrode, and a certain amount of lithium ions are embedded in the Overhang area of ​​the negative electrode. However, during the short-term cycle test, the lithium ions embedded in the Overhang area cannot be completely removed. During the high-temperature cycle process, the lithium ions will gradually move from the Overhang area to the middle diaphragm and gradually participate in the deintercalation. Therefore, in the early stage of the cycle, the battery capacity cannot be fully utilized and gradually increases. After reaching a certain number of cycles, the battery capacity gradually decreases. The cyclic climbing phenomenon of battery capacity will have a certain impact on the performance of battery materials and performance evaluation.

[0004] Summary of the Invention

[0005] The present application provides a method for improving battery cycle ramp-up and a lithium-ion battery.

[0006] According to one aspect of the present application, a method for improving battery cycle ramping is provided, comprising:

[0007] Performing constant-current and constant-voltage charging on the battery to be tested with a preset charging current until the voltage of the battery to be tested reaches the rated voltage and the current of the battery to be tested reaches the target cut-off current;

[0008] The battery to be tested is sequentially discharged twice with a constant current. The method of performing constant current discharge on the battery to be tested includes:

[0009] Allowing the battery to be tested to stand for a first preset time;

[0010] After the rest period is completed, the battery to be tested is discharged at a constant current until the voltage of the battery to be tested reaches a preset cut-off voltage.

[0011] According to another aspect of the present application, a lithium-ion battery is provided, which is applicable to the method for improving battery cycle ramping as described in any embodiment of the first aspect.

[0012] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present application, nor is it intended to limit the scope of the present application. Other features of the present application will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0014] FIG1 is a flow chart of a method for improving battery cycle ramping according to an embodiment of the present application;

[0015] FIG2 is a flow chart of another method for improving battery cycle ramping according to an embodiment of the present application;

[0016] FIG3 is a flow chart of another method for improving battery cycle ramping according to an embodiment of the present application;

[0017] FIG4 is a schematic diagram of a process of applying a method for improving battery cycle ramping provided in an embodiment of the present application to an NCM5 series soft pack battery;

[0018] FIG5 is a cycle performance curve diagram of a soft-pack battery provided according to an embodiment of the present application. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0020] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in a sequence other than those illustrated or described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0021] The present invention provides a method for improving battery cycle ramping. Figure 1 is a flow chart of a method for improving battery cycle ramping provided by the present invention. This embodiment is applicable to improving the cycle ramping phenomenon that occurs in the early stages of the charge and discharge cycle of lithium-ion batteries, and includes the following steps:

[0022] S110 , performing constant-current and constant-voltage charging on the battery to be tested with a preset charging current until the voltage of the battery to be tested reaches the rated voltage and the current of the battery to be tested reaches the target cut-off current.

[0023] Among them, the rated voltage is the rated voltage that the positive electrode material of the battery to be tested can reach by itself. Therefore, when the battery to be tested uses different positive electrode materials, the rated voltage that the battery to be tested needs to reach after the first constant current and constant voltage charging is also different, which is not limited here. The target cutoff current is the charging current of the battery to be tested when charging is completed, which can be set according to the preset charging current and actual needs. In the process of constant current and constant voltage charging of the battery to be tested with a preset charging current, when the voltage of the battery to be tested reaches the rated voltage and the charging current reaches the target cutoff current, it indicates that the battery to be tested has completed the first charge. For example, the preset charging current for constant current and constant voltage charging of the battery to be tested can be 1C, and the target cutoff current can be 0.05C.

[0024] S120, performing two constant current discharges on the battery to be tested in sequence; wherein the method for performing constant current discharge on the battery to be tested includes: allowing the battery to be tested to stand for a first preset time; after the standing time ends, performing constant current discharge on the battery to be tested until the voltage of the battery to be tested reaches a preset cut-off voltage.

[0025] The preset cutoff voltage is the lowest voltage that can be achieved by the positive electrode material selected for the battery under test. After the battery under test is fully charged, the battery under test is discharged at a constant current to complete a charge-discharge cycle. For example, during a constant current discharge of the battery under test, the battery under test is first allowed to rest for a period of time to eliminate polarization within the battery under test. After the rest period, the battery under test is discharged at a constant current until the voltage of the battery under test reaches the preset cutoff voltage, i.e., the battery under test is fully discharged, thereby completing a constant current discharge process of the battery under test.

[0026] After the battery to be tested undergoes a constant current discharge process, that is, the battery to be tested completes a charge and discharge cycle, since the negative electrode is provided with an Overhang region, for the battery to be tested prepared with certain battery materials, there will be a cycle climbing phenomenon at the beginning of the cycle. That is to say, after the battery to be tested undergoes a charge and discharge cycle, the battery capacity does not decrease, but instead increases, that is, the battery capacity after the first discharge is higher than the battery capacity after the first charge, which seriously affects the accuracy of the electrical performance evaluation results of the battery material. Based on this technical problem, the applicant proposes in this embodiment that, after a constant current discharge process, the battery to be tested is subjected to a second constant current discharge to fully activate the lithium ions in the Overhang region of the negative electrode of the battery, so that the battery capacity is fully utilized, thereby improving the cycle climbing phenomenon that occurs in the battery to be tested at the beginning of the cycle and improving the accuracy of the electrical performance evaluation of the battery material.

[0027] The technical solution of this embodiment is to charge the battery to be tested with a preset charging current at a constant current and constant voltage until the voltage of the battery to be tested reaches the rated voltage and the current of the battery to be tested reaches the target cut-off current, and then stop charging. The battery to be tested is then subjected to two constant current discharges; wherein, each time the battery to be tested is discharged at a constant current, the battery to be tested is first left to stand for a first preset time to eliminate the polarization phenomenon generated inside the battery to be tested after charging or discharging; and then the battery to be tested is discharged at a constant current again until the voltage of the battery to be tested reaches the preset cut-off voltage, and then stop discharging. After one constant current discharge, that is, the battery to be tested has undergone a charge and discharge cycle, due to the structure of the battery material, the lithium ions in the negative electrode overhang area cannot be completely released, and the battery capacity shows a cyclic climbing phenomenon of gradually increasing. Therefore, by performing a second constant current discharge on the battery to be tested, the battery capacity can be fully utilized, thereby effectively improving the cyclic climbing phenomenon of the battery capacity and improving the accuracy of the electrical performance evaluation test of the battery material.

[0028] FIG2 is a flow chart of another method for improving battery cycle ramping provided by an embodiment of the present application. Based on the above embodiments, as shown in FIG2 , the method for improving battery cycle ramping provided by this embodiment includes:

[0029] S210 , performing constant-current and constant-voltage charging on the battery to be tested with a preset charging current until the voltage of the battery to be tested reaches the rated voltage and the current of the battery to be tested reaches the target cut-off current.

[0030] S220: Leave the battery to be tested to stand for a first preset time.

[0031] For example, after the battery to be tested is charged with constant current and constant voltage, the polarization phenomenon generated inside the battery is eliminated by leaving the battery to be tested at rest for a period of time to ensure the accuracy of the subsequent discharge of the battery to be tested. Exemplarily, the first preset time is greater than or equal to 5 minutes. If the first preset time for the battery to be tested to remain in a static state is less than 5 minutes, the polarization phenomenon generated inside the battery to be tested may not be completely eliminated due to the fact that the static time is too short; if the first preset time for the battery to be tested to remain in a static state is too long, although the polarization inside the battery can be completely eliminated, it takes too much time, which seriously affects the efficiency of the electrical performance evaluation test of the battery material. For example, in this embodiment, the first preset time for the battery to be tested to remain at rest is set to 5 minutes, so that the polarization inside the battery can be completely eliminated in a shorter time.

[0032] S230 , after the rest period is completed, performing a first constant current discharge on the battery to be tested at a first discharge current until the voltage of the battery to be tested reaches a first preset cut-off voltage.

[0033] Exemplarily, the first discharge current is less than or equal to 1C. A first constant current discharge is performed on the battery under test at the first discharge current, and the discharge is stopped when the voltage of the battery under test reaches a first preset cutoff voltage. The preset cutoff voltage includes a first preset cutoff voltage; the first preset cutoff voltage is the voltage of the battery under test when the first constant current discharge is completed.

[0034] S240: Let the battery to be tested stand for the first preset time again.

[0035] For example, after charging or discharging a battery under test, it is necessary to rest the battery under test for a period of time to eliminate polarization generated within the battery and ensure the accuracy of subsequent tests. For example, the rest period after the first discharge can be the same as the rest period after charging, both being a first preset time. This can fully eliminate internal polarization in the battery while shortening the test time and improving the efficiency of the battery material electrical performance evaluation test.

[0036] S250 , after the rest period is completed, performing a second constant current discharge on the battery to be tested with a second discharge current until the voltage of the battery to be tested reaches a second preset cut-off voltage.

[0037] For example, a second constant current discharge is performed with a second discharge current, and the discharge is stopped when the voltage of the battery to be tested reaches the second preset cut-off voltage. This can fully activate the lithium ions in the overhang area of ​​the battery, so that the battery capacity of the battery to be tested is fully utilized, and the battery capacity gradually decreases, thereby improving the cycle climbing phenomenon of the battery. Exemplarily, the second discharge current is less than or equal to 1C, and the second discharge current is less than or equal to the first discharge current. When the discharge current of the battery to be tested undergoes two constant current discharges and satisfies the above relationship, the battery cycle climbing phenomenon can be effectively improved or even eliminated in a shorter discharge time, truly reflecting the electrical properties of the battery material.

[0038] The preset cutoff voltage also includes a second preset cutoff voltage; the second preset cutoff voltage is the voltage of the battery under test upon completion of the second constant-current discharge. For example, by setting the second preset cutoff voltage to be less than or equal to the first preset cutoff voltage, the cyclic ramp-up phenomenon of the battery under test can be effectively improved after a single constant-current constant-voltage charge and two consecutive constant-current discharges of the battery under test. This eliminates the need to adjust the structure of the battery under test, thereby reducing testing costs.

[0039] FIG3 is a flow chart of another method for improving battery cycle ramping provided by an embodiment of the present application. Based on the above embodiments, as shown in FIG3 , the method for improving battery cycle ramping provided by this embodiment includes:

[0040] S310 , leaving the battery to be tested to stand for a second preset time.

[0041] For example, before testing the battery to be tested, the battery to be tested is allowed to stand for a period of time to eliminate the internal polarization of the battery, so as to ensure the safety of the battery and the accuracy of the test in subsequent tests. Exemplarily, the time for the battery to be tested to stand before the test can be a second preset time, and the second preset time is 5 to 60 minutes. If the second preset time is less than 5 minutes, the internal polarization of the battery to be tested may not be completely eliminated due to the short standing time; if the second preset time is greater than 60 minutes, although the internal polarization of the battery to be tested is completely eliminated, it takes a long time, which greatly reduces the efficiency of the electrical performance evaluation test of the battery material. For example, the second preset time is 10 minutes, which can shorten the time while completely eliminating the internal polarization of the battery and improve the test efficiency.

[0042] S320 , performing constant-current and constant-voltage charging on the battery to be tested with a preset charging current until the voltage of the battery to be tested reaches the rated voltage and the current of the battery to be tested reaches the target cut-off current.

[0043] S330, performing two constant current discharges on the battery to be tested in sequence; wherein, the method for performing constant current discharge on the battery to be tested includes: allowing the battery to be tested to stand for a first preset time; after the standing time ends, performing constant current discharge on the battery to be tested until the voltage of the battery to be tested reaches a preset cut-off voltage.

[0044] In one embodiment, NCM5 soft-pack batteries and conventional soft-pack batteries in a conventional test process are used as examples. The method for improving battery cycle ramping provided by any embodiment of the present application is applied to each soft-pack battery to test the electrical properties of the soft-pack battery material. Figure 4 is a flow chart of a method for improving battery cycle ramping provided by an embodiment of the present application applied to NCM5 soft-pack batteries. As shown in Figure 4, the operation process is as follows:

[0045] S1. Keep the NCM5 series soft pack battery in a static state for 60 minutes;

[0046] S2. Charge the NCM5 soft-pack battery at a constant current and constant voltage with a charging current of 1C until the voltage of the NCM5 soft-pack battery reaches 4.4V and the charging current reaches 0.05C, then stop charging.

[0047] S3. Keep the NCM5 series soft pack battery in a static state for 5 minutes;

[0048] S4, discharge the NCM5 series soft pack battery at a constant current of 1C until the voltage of the NCM5 series soft pack battery reaches 2.8V, and then stop discharging;

[0049] S5. Keep the NCM5 series soft pack battery in a static state for 5 minutes;

[0050] S6. Discharge the NCM5 soft-pack battery at a constant current of 0.04C until the voltage of the NCM5 soft-pack battery reaches 2.8V, and then stop discharging.

[0051] S7. Keep the NCM5 series soft pack battery in a static state for 5 minutes;

[0052] S8. Perform a charge-discharge cycle test on the NCM5 series soft-pack battery and record the relevant cycle data as Example A1.

[0053] Among them, steps S1 to S6 are pre-charge operations before the charge and discharge cycle test. According to the above steps S1 to S8, the same pre-charge operation and charge and discharge cycle test are performed on ordinary soft-pack batteries, and the relevant cycle data are recorded as Example B1. Select the NCM5 soft-pack batteries in the same group as the NCM5 soft-pack batteries in Example A1, and directly perform the charge and discharge cycle test of step S8 on the batteries without performing the pre-charge operation of steps S1 to S6, and record the relevant cycle data as Example A2. Similarly, select the ordinary soft-pack batteries in the same group as the ordinary soft-pack batteries in Example B1, and directly perform the charge and discharge cycle test of step S8 on the batteries without performing the pre-charge operation of steps S1 to S6, and record the relevant cycle data as Example B2.

[0054] According to the relevant cycle data of Example A1, Example A2, Example B1 and Example B2, the cycle test results of each soft-pack battery are obtained. Figure 5 is a cycle performance curve diagram of a soft-pack battery provided in an embodiment of the present application, see Figure 5, wherein the horizontal axis of the curve diagram is the number of cycles, and the vertical axis is the battery capacity retention rate. Curve 01 represents the cycle performance curve of Example A1, curve 02 represents the cycle performance curve of Example A2, curve 03 represents the cycle performance curve of Example B1, and curve 04 represents the cycle performance curve of Example B2. It can be seen from Figure 5 that if the soft-pack battery is pre-charged before the charge and discharge cycle test, as the number of cycles increases, the battery capacity of the soft-pack battery that has undergone the pre-charge operation gradually decreases from the initial 100%, and the battery capacity does not show a cycle climbing phenomenon. Referring to curve 01 and curve 03 in Figure 5, their cycle performance curves almost overlap. For soft-pack batteries that were directly subjected to charge and discharge cycle testing without pre-charging, in the early stages of the cycle test with a small number of cycles, as shown in curves 02 and 04, the battery capacity of the soft-pack battery increased during the charge and discharge cycle, a phenomenon known as cycle ramping. After a certain number of cycles, for example, about 20 cycles, the battery capacity of the soft-pack battery gradually decreased. Furthermore, curves 02 and 04 show that the increase in battery capacity produced by curve 02 is smaller than that produced by curve 04, indicating that the NCM5 series soft-pack batteries have better cycle performance than ordinary soft-pack batteries.

[0055] In summary, the method for improving battery cycle climbing provided in any embodiment of the present application can effectively improve or even eliminate the phenomenon of battery capacity cycle climbing generated by soft-pack batteries in the early stage of the charge and discharge cycle, thereby truly reflecting the electrical properties of the battery material and improving the accuracy of the electrical performance evaluation results of the battery material.

[0056] The embodiments of the present application also provide a lithium-ion battery. For example, the lithium-ion battery includes a ternary system battery, a lithium iron phosphate system battery and / or a lithium cobalt oxide system battery. The method for improving battery cycle climbing provided in any embodiment of the present application can be widely applied to ternary system batteries, lithium iron phosphate system batteries and / or lithium cobalt oxide system batteries. By performing a pre-charge operation of constant current and constant voltage charging and two constant current discharges on the battery before the battery is subjected to a charge and discharge cycle test, the problem that the lithium ions in the negative electrode overhang area cannot be completely released due to the structure of the battery material and other reasons, and the battery capacity cycle climbing occurs in the early stage of the charge and discharge cycle can be effectively improved, so that the cycle test results truly reflect the electrical properties of the battery material and improve the accuracy of the electrical performance evaluation. In addition, there is no need to adjust the battery structure, which reduces the testing cost.

[0057] The above specific embodiments do not constitute a limitation on the scope of protection of this application. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors.

Claims

1. A method for improving battery cycle ramping, comprising: Performing constant current and constant voltage charging on the battery to be tested with a preset charging current until the voltage of the battery to be tested reaches the rated voltage and the current of the battery to be tested reaches the target cut-off current; The battery to be tested is discharged at a constant current twice in sequence; wherein the method for discharging the battery to be tested at a constant current comprises: Allowing the battery to be tested to stand for a first preset time; After the standing still is completed, the battery to be tested is discharged at a constant current until the voltage of the battery to be tested reaches a preset cut-off voltage.

2. The method for improving battery cycle ramping according to claim 1, wherein: The preset cut-off voltage includes a first preset cut-off voltage and a second preset cut-off voltage; The step of performing two constant current discharges on the battery to be tested in sequence includes: Allowing the battery to be tested to stand for a first preset time; After the standing still is completed, performing a first constant current discharge on the battery to be tested with a first discharge current until the voltage of the battery to be tested reaches the first preset cut-off voltage; Allowing the battery to be tested to stand for a first preset time again; After the resting is completed, the battery to be tested is subjected to a second constant current discharge with a second discharge current until the voltage of the battery to be tested reaches the second preset cut-off voltage.

3. The method for improving battery cycle ramping according to claim 2, wherein: The second preset cut-off voltage is less than or equal to the first preset cut-off voltage.

4. The method for improving battery cycle ramping according to claim 3, wherein: The first discharge current and the second discharge current are both less than or equal to 1C, and the second discharge current is less than or equal to the first discharge current.

5. The method for improving battery cycle ramping according to claim 2, wherein: The first preset time is greater than or equal to 5 minutes.

6. The method for improving battery cycle ramping according to claim 1, wherein: The preset charging current is 1C, and the target cut-off current is 0.05C.

7. The method for improving battery cycle climbing according to claim 1, before the battery to be tested is charged with constant current and constant voltage, further comprising: The battery to be tested is left to stand for a second preset time.

8. The method for improving battery cycle ramping according to claim 7, wherein: The second preset time is 5 to 60 minutes.

9. The method for improving battery cycle ramping according to claim 8, wherein: The second preset time is 10 minutes.

10. A lithium ion battery, suitable for the method for improving battery cycle ramp-up as claimed in any one of claims 1 to 9.

11. The lithium ion battery according to claim 10, wherein: The lithium-ion battery includes a ternary system battery, a lithium iron phosphate system battery and / or a lithium cobalt oxide system battery.

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