A method for detecting activation degree of lithium battery

Abstract

The embodiment of the present invention discloses a method for detecting the activation level of a lithium battery. By performing two charge-discharge cycles on the battery and comparing the corresponding voltage difference between the two charge-discharge cycles, the activation state of the battery can be determined. Thus, by adopting the technical solution of the embodiment of the present invention, the time for detecting the activation level of a lithium battery can be effectively shortened, the detection efficiency can be improved, and testing resources can be saved. At the same time, the method for detecting the activation level of a lithium battery in the embodiment of the present invention avoids destructive disassembly of the battery, reduces battery waste, and, compared with the method of judging the activation level of a lithium battery based on subjective experience, reduces the interference of human factors in the test results.

Description

Technical Field

[0001] The present invention relates to the field of battery testing, and in particular to a method for detecting the activation degree of a lithium battery. Background Art

[0002] After the lithium battery is assembled, it needs to be subjected to high-temperature static, low-current charging, high-temperature aging and room-temperature aging steps to form the battery and activate the positive and negative electrode materials inside the battery. If the lithium battery is not fully activated, the performance will be significantly reduced. There are two conventional methods for detecting the degree of activation: one detection method is to disassemble the battery after formation and observe the battery electrolyte infiltration and the electrode interface to determine the degree of activation. On the one hand, this detection method will cause battery waste. On the other hand, because the degree of activation relies on subjective experience, the judgment result is greatly affected by human factors; the other detection method is to conduct a series of performance tests (such as rate tests, cycle tests, etc.) and make comparative judgments based on the test results. The disadvantage of this method is that the test cycle is long. Summary of the Invention

[0003] An object of the embodiments of the present invention is to provide a method for detecting the activation degree of a lithium battery, which can overcome at least one of the above-mentioned defects in the prior art.

[0004] The method for detecting the activation degree of a lithium battery according to an embodiment of the present invention includes the following steps: charging the battery to 100% state of charge at a first rate, and discharging the battery to the first state of charge at a second rate after standing for a first time; performing a first charge and discharge cycle on the battery to obtain a first voltage difference; performing a second charge and discharge cycle on the battery to obtain a second voltage difference; and determining the activation state of the battery based on the first voltage difference and the second voltage difference, wherein when the first voltage difference is less than or equal to the second voltage difference, the activation state of the battery is determined to be completed activation; wherein the charge and discharge cycle includes the following steps: charging the battery to the second state of charge at a second rate after standing for a second time, and obtaining an average voltage during the charging process, wherein the second state of charge is greater than the first state of charge; and, discharging the battery to the first state of charge at the second rate after standing for a third time, and obtaining an average voltage during the discharge process; the voltage difference is the difference between the average voltage during the discharge process and the average voltage during the charging process in the corresponding charge and discharge cycle.

[0005] Furthermore, the first time, the second time and the third time are equal.

[0006] Furthermore, the first time, the second time and the third time are greater than or equal to one hour.

[0007] Furthermore, the first time, the second time and the third time are one hour.

[0008] Furthermore, the first magnification is 1 / 3C.

[0009] Furthermore, the second magnification is 1C.

[0010] Furthermore, the positive electrode active material of the battery includes a ternary or binary material with a single crystal structure, and the negative electrode active material of the battery includes a primary particle graphite material.

[0011] Furthermore, the charging of the battery to 100% state of charge at the first rate and the charging of the battery to the second state of charge at the second rate are both constant current and constant voltage charging.

[0012] Furthermore, discharging the battery at the second rate to the first state of charge is constant current discharge.

[0013] An embodiment of the present invention provides a method for detecting the activation level of a lithium battery. By subjecting the battery to two charge-discharge cycles and comparing the corresponding voltage differences between the two charge-discharge cycles, the activation state of the battery can be determined. Thus, by adopting the technical solution of the embodiment of the present invention, the time required for detecting the activation level of a lithium battery can be effectively shortened, detection efficiency can be improved, and testing resources can be saved. Furthermore, the method for detecting the activation level of a lithium battery in the embodiment of the present invention avoids destructive disassembly of the battery, reducing battery waste. Furthermore, compared to methods that use subjective experience to determine the activation level of a lithium battery, it reduces the risk of human interference in the test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0015] Figure 1 4 is a flow chart of a method for detecting activation degree of a lithium battery according to an embodiment of the present invention.

[0016] Figure 2 Flowchart of the charge and discharge cycle of an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The present invention is described below based on the following embodiments, but the present invention is not limited to these embodiments. In the detailed description of the present invention below, certain specific details are described in detail. Those skilled in the art can fully understand the present invention without these details. To avoid obscuring the essence of the present invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0018] Furthermore, persons of ordinary skill in the art will appreciate that the figures provided herein are for illustration purposes only and are not necessarily drawn to scale.

[0019] Unless the context clearly requires otherwise, words like “include”, “comprising” and the like throughout this application should be interpreted as including rather than exclusive or exhaustive; that is, as meaning “including but not limited to”.

[0020] In the description of the present invention, it should be understood that the terms "first", "second", etc. are used for descriptive purposes only and should not be understood to indicate or imply relative importance. In addition, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0021] In this application, rate refers to the current required to charge or discharge a battery to its rated capacity within a specified time. It is a measure of the speed of charge or discharge. The rate is numerically equal to a multiple of the battery's rated capacity and is typically represented by the letter C. For example, a battery rated at 2200mA·h is discharged at a 1C discharge rate for one hour, resulting in a discharge current of 2200mA.

[0022] In this application, the state of charge (SOC) refers to the ratio of the remaining capacity of a secondary battery to its total capacity, usually expressed as a percentage. When SOC is 0%, it means the battery is fully discharged, and when SOC is 100%, it means the battery is fully charged.

[0023] Figure 1 The flowchart of the method for detecting the activation level of a lithium battery according to an embodiment of the present invention is provided. The method can be used to detect the activation state of a lithium battery after the formation process. Alternatively, the method can be applied to detect the activation level of a lithium battery whose positive electrode active material comprises a single-crystal ternary or binary material and whose negative electrode active material comprises primary graphite particles.

[0024] Reference Figure 1 The lithium battery activation degree detection method according to the embodiment of the present invention includes the following steps S101 to S104:

[0025] Step S101 : charging the battery to 100% state of charge at a first rate, and discharging the battery to the first state of charge at a second rate after standing for a first time.

[0026] Step S102: performing a first charge and discharge cycle on the battery to obtain a first voltage difference.

[0027] Step S103: performing a second charge and discharge cycle on the battery to obtain a second voltage difference.

[0028] Step S104: determining the activation state of the battery according to the first voltage difference and the second voltage difference.

[0029] In step S101, the battery to be tested is charged to a state of charge (SOC) of 100% at a first rate. Preferably, the charging process is constant current and constant voltage charging. After the battery is left to stand for a first time, the battery is discharged to a first state of charge at a second rate. In this embodiment, the first rate is 1 / 3C and the second rate is 1C. The first state of charge is greater than or equal to 0% state of charge and less than 100% state of charge. In other words, assuming that the first state of charge is X% SOC, 0≤X<100. Optionally, the first state of charge is greater than or equal to 40% state of charge and less than or equal to 60% state of charge, that is, 40≤X<60.

[0030] After step S101 , the battery is subjected to at least two charge and discharge cycles, which in this embodiment are steps S102 and S103 .

[0031] In step S102 and step S103, the battery is subjected to a first charge-discharge cycle and a second charge-discharge cycle in sequence, and the voltage differences corresponding to the two charge-discharge cycles are obtained respectively.

[0032] Figure 2 Flowchart of the charge and discharge cycle of the embodiment of the present invention. Figure 2 In this embodiment, each charge-discharge cycle in step S102 and step S103 includes the following steps S201 to S202:

[0033] Step S201: After standing for a second time, charge the battery at a second rate to a second state of charge, and obtain an average voltage during the charging process.

[0034] Step S202: After standing for a third time, discharge the battery at a second rate to a first state of charge, and obtain an average voltage during the discharge process.

[0035] In step S201, the discharged battery is left to stand for a second time, wherein the "discharged battery" in the first charge and discharge cycle refers to the battery after completing step S101, and in the second charge and discharge cycle refers to the battery after completing the first charge and discharge cycle (i.e., step S102). Then, the battery is charged to a second state of charge at a second rate, and the charging voltage during the charging process is detected to obtain the average voltage of the charging process. The second state of charge is greater than 0% state of charge and less than or equal to 100% state of charge, and at the same time, the second state of charge is greater than the first state of charge. In other words, assuming that the first state of charge is X% SOC and the second state of charge is Y% SOC, then 0≤X<Y≤100. Optionally, the second state of charge is greater than or equal to 40% state of charge and less than or equal to 60% state of charge, that is, 40≤X<Y≤60.

[0036] In step S202, the battery, which has completed step S202 in the charge-discharge cycle, is allowed to rest for a third time. After resting, the battery is discharged at a second rate to a first state of charge, and the discharge voltage during the discharge process is detected to obtain an average voltage during the discharge process. Optionally, the discharge process is constant current charging.

[0037] In this embodiment, the first time, the second time, and the third time can be selected as needed. Optionally, the first time, the second time, and the third time can be equal to facilitate process control. Optionally, the first time, the second time, and the third time are greater than or equal to one hour to provide sufficient time for the electrochemical reaction within the battery, while reducing the impact of the battery voltage hysteresis on the test results and ensuring the accuracy of the test results. Further, optionally, the first time, the second time, and the third time are equal to one hour, which can not only ensure a certain degree of accuracy in the test results, but also shorten the time required for detection and improve detection efficiency.

[0038] After completing the corresponding charge and discharge cycle (the first charge and discharge cycle or the second charge and discharge cycle), the voltage difference in the corresponding charge and discharge cycle can be obtained. In this embodiment, the voltage difference is the difference between the average voltage of the discharge process and the average voltage of the charge process in the corresponding charge and discharge cycle. The voltage difference in the charge and discharge cycle can be calculated by the formula ΔV=V D -V C Calculate. Where △V is the voltage difference, V D is the average voltage of the discharge process in the corresponding charge and discharge cycle, V C is the average voltage of the charging process in the corresponding charge and discharge cycle.

[0039] After completing two charge and discharge cycles (ie, steps S102 and S103 ), a first voltage difference in the first charge and discharge cycle and a second voltage difference in the second charge and discharge cycle can be obtained.

[0040] In step S104, the activation state of the battery is determined according to the first voltage difference and the second voltage difference. Specifically, the activation state of the battery can be determined by comparing the first voltage difference and the second voltage difference.

[0041] During the formation process, a series of electrochemical reactions occur in the battery, forming a passivation layer covering the electrode surface. This passivation layer is called the solid electrolyte interface (SEI) film. In this application, "complete activation" means that a stable SEI film has formed on the electrode surface, and "incomplete activation" means that a stable SEI film has not yet formed on the electrode surface.

[0042] A fully activated battery forms a stable SEI film, and as the number of charge and discharge cycles increases, the internal resistance of the battery tends to stabilize or show an upward trend, which in turn causes the voltage difference in the second charge and discharge cycle to be greater than or equal to the voltage difference in the first charge and discharge cycle. When the battery is not fully activated, since a complete and stable SEI film has not yet formed on the electrode surface, the SEI film impedance is large, and the SEI film will continue to form during the charge and discharge cycle, causing the internal resistance of the battery to show a downward trend as the number of charge and discharge cycles increases, which in turn causes the voltage difference in the second charge and discharge cycle to be smaller than the voltage difference in the first charge and discharge cycle.

[0043] Based on the above principles, in step S104, the activation state of the lithium battery can be determined by comparing the first voltage difference and the second voltage difference. Specifically, when the first voltage difference is less than or equal to the second voltage difference, the battery activation state can be determined to be complete; when the first voltage difference is greater than the second voltage difference, the battery activation state can be determined to be incomplete.

[0044] Table 1 below shows the test results of lithium batteries that have undergone a formation process (including activated and unactivated lithium batteries) using the lithium battery activation degree detection method according to an embodiment of the present invention. In the test, the first rate is 1 / 3C, the second rate is 1C, and the first, second, and third times are 1 hour. In Table 1, V C1 is the average voltage of the charging process in the first charge and discharge cycle, V D1 is the average voltage of the discharge process in the first charge and discharge cycle, V C2 is the average voltage of the charging process in the second charge and discharge cycle, V D2 is the average voltage of the discharge process in the second charge and discharge cycle, △V1 is the first voltage difference, and △V2 is the second voltage difference.

[0045] Table 1

[0046]

[0047] As shown in Table 1, for battery number 1, during the test, charge and discharge cycles were performed within the SOC range of 45% SOC-55% SOC, and the test result was that the first voltage difference was less than the second voltage difference. According to the determination method of the embodiment of the present invention, the activation degree of the lithium battery was determined to be completed. For battery number 2, during the test, charge and discharge cycles were performed within the SOC range of 40% SOC-60% SOC, and the test result was that the first voltage difference was greater than the second voltage difference. According to the determination method of the embodiment of the present invention, the activation degree of the lithium battery was determined to be incomplete. For battery number 3, during the test, charge and discharge cycles were performed within the SOC range of 0% SOC-100% SOC, and the test result was that the first voltage difference was greater than the second voltage difference. According to the determination method of the embodiment of the present invention, the activation degree of the lithium battery was determined to be incomplete. For the batteries numbered 1-3 that were tested, the activation degree of the batteries was verified by other detection methods, and the verification results were consistent with the results determined by the lithium battery activation degree detection method of the embodiment of the present invention. At the same time, as shown in Table 1, charging and discharging the lithium battery within the SOC range of 40% SOC-60% SOC can make the first voltage difference and the second voltage difference of the lithium battery that has not been fully activated have a certain difference. If the detection equipment has high accuracy, the battery can be tested by charging and discharging within a partial SOC range, without the need for a full charge and discharge cycle between 0% SOC and 100% SOC, which can improve detection efficiency.

[0048] After step S104, for batteries determined to have completed activation, the formation process can be terminated and the next manufacturing step can be entered. For batteries determined to have not completed activation, the formation process can be continued.

[0049] This embodiment illustrates the principle of the lithium battery activation degree detection method by performing two charge-discharge cycles on the battery and comparing the voltage difference between the two cycles. However, it is understood that, depending on the desired error rate of the detection results, the number of charge-discharge cycles can be increased and the voltage differences of multiple charge-discharge cycles can be compared.

[0050] The method for detecting the activation level of a lithium battery according to an embodiment of the present invention can determine the activation state of a battery by subjecting the battery to two charge-discharge cycles and comparing the corresponding voltage differences between the two charge-discharge cycles. Therefore, compared to traditional detection methods based on performance test results, the method for detecting the activation level of a lithium battery according to an embodiment of the present invention can effectively shorten the time required to detect the activation level of a lithium battery, is simple to operate, improves detection efficiency, and conserves testing resources. Furthermore, compared to methods that involve disassembling the battery and making judgments based on subjective experience, the method for detecting the activation level of a lithium battery according to an embodiment of the present invention avoids damaging and disassembling the battery, reduces battery waste, and reduces the risk of human interference in the test results.

[0051] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for detecting the activation degree of a lithium battery, characterized in that: include: charging the battery to 100% state of charge at a first rate, and discharging the battery to the first state of charge at a second rate after standing for a first time; Performing a first charge and discharge cycle on the battery to obtain a first voltage difference; performing a second charge-discharge cycle on the battery to obtain a second voltage difference; as well as determining an activation state of the battery according to the first voltage difference and the second voltage difference, wherein when the first voltage difference is less than or equal to the second voltage difference, determining that the activation state of the battery is completed; Wherein, the charge and discharge cycle includes: After standing for a second time, charging the battery at a second rate to a second state of charge, and obtaining an average voltage during the charging process, wherein the second state of charge is greater than the first state of charge; and After standing for a third time, discharging the battery at a second rate to a first state of charge, and obtaining an average voltage during the discharge process; The voltage difference is the difference between the average voltage during the discharge process and the average voltage during the charge and discharge process in the corresponding charge and discharge cycle.

2. The method according to claim 1, characterized in that The first time, the second time and the third time are equal.

3. The method according to claim 1, characterized in that The first time, the second time, and the third time are greater than or equal to one hour.

4. The method according to claim 1, wherein The first time, the second time, and the third time are one hour.

5. The method according to claim 1, wherein The first state of charge and the second state of charge are greater than or equal to 40% state of charge and less than or equal to 60% state of charge.

6. The method according to claim 1, characterized in that The first magnification is 1 / 3C.

7. The method according to claim 1, characterized in that The second magnification is 1C.

8. The method according to claim 1, characterized in that The positive electrode active material of the battery includes a ternary or binary material with a single crystal structure, and the negative electrode active material of the battery includes a primary particle graphite material.

9. The method according to claim 1, characterized in that The charging of the battery to 100% state of charge at the first rate and the charging of the battery to the second state of charge at the second rate are both constant current and constant voltage charging.

10. The method according to claim 1, characterized in that Discharging the battery to the first state of charge at the second rate is constant current discharge.

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