A method, device, and battery for detecting self-discharge of a lithium-ion battery

Abstract

The present invention discloses a method, device and battery for detecting self-discharge of a lithium-ion battery. The method includes the following steps: measuring the voltage drop and capacity loss of the battery during the standing time; approximately obtaining the self-discharge current by using the open-circuit voltage-capacity curve of the battery during constant current charge and discharge; obtaining the ratio of the voltage drop to the standing time by the K-value method to estimate the magnitude of the self-discharge current; analyzing the open-circuit voltage-capacity curve of the battery to determine the cause of self-discharge. The present invention provides a method for quickly judging the degree of self-discharge of a lithium-ion battery and the cause of self-discharge, which is convenient for subsequent classification of the self-discharge level of products or guiding the subsequent research and development improvement of products.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly to a method, a device, and a battery for detecting self-discharge of a lithium-ion battery. Background Art

[0002] Currently, the contradiction between energy and the environment forces people to search for clean energy, and lithium-ion batteries have become pioneers and market leaders due to their high energy density in micro-batteries. This is a compact electrochemical energy storage device with a rechargeable cycle life that can easily exceed 1000 times. Its size can range from a few micrometers to large batteries, and it can power computer memory chips, communication devices, color movies, and electric vehicles (EVs). Unfortunately, how to manage the consistency of lithium-ion batteries is a major problem, and any dust, impurities, or other subtle differences during the production process can cause a Waterloo-like decline in battery performance. Among the consistency problems of lithium-ion batteries, the self-discharge problem has always been one of the headaches for many researchers.

[0003] Traditional self-discharge inspection methods are the "remaining capacity method" or the "K-value method". The former can accurately measure the self-discharge current but is time-consuming and laborious, seriously affecting production efficiency. The latter can quickly obtain the magnitude of self-discharge. However, since the "K-value method" charges the battery to a certain voltage V1 and then measures the voltage V2 after standing for a period of time t, and k = (V1 - V2) / t, that is, it distinguishes the degree of self-discharge by the voltage drop within the same time. But there is a serious problem. Since there is a "plateau region" during the charge and discharge process of the battery, that is, the voltage change is very small, this makes the test of the "K-value method" need to avoid these plateau regions.

[0004] The "remaining capacity method" means that the battery is charged and discharged twice. The first discharge is carried out at voltage V1, and the discharged capacity Q1 is obtained when it stops. Then the battery is charged to V1 and left standing for a period of time t1, and then discharged. The discharged capacity this time is Q2. Then the self-discharge current ISD = (Q1 - Q2) / t1. Compared with the "K-value method", this method can accurately measure the self-discharge current but is time-consuming and laborious.

[0005] Although the two methods have their own advantages and disadvantages, they can only be used to distinguish the degree of self-discharge and cannot determine whether the cause of self-discharge is internal short circuit or side reactions of the positive or negative electrode. And the cause of self-discharge is very important for the classification of the self-discharge grade of products on the lithium-ion battery production line or for the subsequent research and development improvement of products. Summary of the Invention

[0006] The object of the present invention is to provide a method, a device and a battery for detecting the self-discharge of a lithium-ion battery, which can quickly judge the degree of self-discharge of a lithium-ion battery and the cause of self-discharge, and is convenient for subsequent classification of the self-discharge level of products or guiding the subsequent research and development improvement of products.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for detecting the self-discharge of a lithium-ion battery, the method comprising the following steps:

[0009] Measure the voltage drop and capacity loss of the battery during the standing time;

[0010] Approximate the open-circuit voltage-capacity curve of the battery during constant current charge and discharge to obtain the self-discharge current;

[0011] Obtain the ratio of the voltage drop to the standing time by the K-value method to estimate the magnitude of the self-discharge current;

[0012] Analyze the open-circuit voltage-capacity curve of the battery to determine the cause of self-discharge.

[0013] In the above technical solution, a reference electrode is used to obtain the self-discharge current and voltage drop.

[0014] In the above technical solution, the self-discharge current and voltage drop are obtained by differential voltage analysis.

[0015] In the above technical solution, the causes of the self-discharge include internal physical short circuit or positive / negative chemical self-discharge.

[0016] In the above technical solution, analyzing the open-circuit voltage-capacity curve of the battery to determine the cause of self-discharge includes:

[0017] When I 正极自放电 ≈I 负极自放电 , the self-discharge mode is physical self-discharge;

[0018] When I 正极自放电 >I 负极自放电 , the self-discharge mode is positive chemical self-discharge;

[0019] When I 正极自放电 <I 负极自放电 , the self-discharge mode is negative chemical self-discharge.

[0020] The present invention provides a test device for testing the cause of self-discharge of a lithium-ion battery, the device comprising:

[0021] A voltage measurement unit for measuring the open-circuit voltage of the battery;

[0022] A capacity measurement unit for measuring the capacity loss of the battery;

[0023] A time control unit for controlling the standing time of the battery;

[0024] A data processing unit for calculating the self-discharge current, analyzing the open-circuit voltage-capacity curve of the battery, and determining the cause of self-discharge.

[0025] In the above technical solution, the data processing unit obtains the self-discharge current and voltage drop through a reference electrode or a differential voltage method.

[0026] In the above technical solution, the data processing unit analyzes the open-circuit voltage-capacity curve of the battery to determine the cause of self-discharge, including:

[0027] When I 正极自放电 ≈I 负极自放电 , the self-discharge mode is physical self-discharge;

[0028] When I 正极自放电 >I 负极自放电 , the self-discharge mode is positive chemical self-discharge;

[0029] When I 正极自放电 <I 负极自放电 , the self-discharge mode is negative chemical self-discharge.

[0030] The present invention provides a lithium-ion battery, including: calculating the self-discharge current and analyzing the cause of self-discharge through the detection method of self-discharge of the lithium-ion battery as described above.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] The present invention provides a detection method, device, and battery for self-discharge of a lithium-ion battery, measuring the voltage drop and capacity loss of the battery during the standing time, approximately obtaining the self-discharge current by using the open-circuit voltage-capacity curve of the battery during constant current charge and discharge, obtaining the ratio of the voltage drop to the standing time through the K value method, estimating the magnitude of the self-discharge current, analyzing the open-circuit voltage-capacity curve of the battery, and determining the cause of self-discharge. The present invention can significantly improve the detection efficiency, and at the same time can judge the cause of self-discharge, providing an important basis for the grade classification and R & D improvement of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic flow chart provided by an embodiment of the present invention.

[0034] Figure 2 It is a schematic diagram of the differential voltage method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. 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.

[0036] The present invention provides a method for detecting the self-discharge of a lithium-ion battery, which can quickly judge the degree of self-discharge of a lithium-ion battery and the cause of self-discharge, facilitating the subsequent classification of the self-discharge level of products or guiding the subsequent research and development improvement of products.

[0037] Specifically, this method includes the following steps:

[0038] Step S1: Measure the voltage drop and capacity loss of the battery during the static time.

[0039] Step S2: Approximately obtain the self-discharge current by using the open-circuit voltage-capacity curve of the battery during constant current charge and discharge.

[0040] Step S3: Obtain the ratio of the voltage drop to the static time through the K-value method to estimate the magnitude of the self-discharge current.

[0041] Step S4: Analyze the open-circuit voltage-capacity curve of the battery to determine the cause of self-discharge.

[0042] Generally, in mathematical form:

[0043]

[0044] Therefore:

[0045]

[0046] Among them, I 自放电 represents the self-discharge current, dt 自放电 represents the static time during the self-discharge test, dQ 自放电 is the capacity consumed by self-discharge during this time, and dU 自放电 is the voltage drop caused by self-discharge during this time. Therefore, only the product of and needs to be calculated separately, and the product is the self-discharge current.

[0047] Self-discharge is actually a discharge with a relatively small current. When the discharge current I 放电 is comparable to the magnitude of the self-discharge current I 自放电 :

[0048]

[0049] Approximated through the open-circuit voltage-capacity curve of the circuit during constant-current charge and discharge and Generally, the smaller the current during constant-current charge and discharge, the more accurately it can be detected. In this application, the current is selected as 0.01c.

[0050] while it can be measured by the K-value method, obtaining:

[0051]

[0052] Thus, through the magnitude of the self-discharge current can be estimated.

[0053] Since the open-circuit voltage-capacity curve of the battery is composed of the difference between the positive electrode voltage-capacity curve and the negative electrode voltage-capacity curve. Expanding Equation (4) to the positive electrode voltage-capacity curve and the negative electrode voltage-capacity curve, we get:

[0054]

[0055] Furthermore, by analyzing the open-circuit voltage-capacity curve of the battery, the causes of self-discharge are determined, including:

[0056] When I 正极自放电 ≈I 负极自放电 , the self-discharge mode is physical self-discharge.

[0057] When I 正极自放电 >I 负极自放电 , the self-discharge mode is positive electrode chemical self-discharge.

[0058] When I 正极自放电 <I 负极自放电 , the self-discharge mode is negative electrode chemical self-discharge.

[0059] Among them it can be obtained by embedding a reference electrode in the battery. Since the detection result of the reference electrode is relatively accurate, it is suitable for studying and analyzing the self-discharge of the battery. Or, as Figure 2 shown, by calculating the difference value of the voltage of the battery through differential voltage analysis (DVA), the self-discharge current and voltage drop are obtained for rapid screening.

[0060] Based on the same inventive concept, this application provides a test device for testing the reasons for the self-discharge of lithium-ion batteries. This device includes:

[0061] A voltage measurement unit for measuring the open-circuit voltage of the battery;

[0062] A capacity measurement unit for measuring the capacity loss of the battery;

[0063] A time control unit for controlling the standing time of the battery;

[0064] A data processing unit for calculating the self-discharge current, analyzing the open-circuit voltage-capacity curve of the battery, and determining the cause of self-discharge.

[0065] The data processing unit obtains the self-discharge current and voltage drop through a reference electrode or a differential voltage method.

[0066] The data processing unit analyzes the open-circuit voltage-capacity curve of the battery and determines the cause of self-discharge, including:

[0067] When I 正极自放电 ≈I 负极自放电 , the self-discharge mode is physical self-discharge;

[0068] When I 正极自放电 >I 负极自放电 , the self-discharge mode is positive chemical self-discharge;

[0069] When I 正极自放电 <I 负极自放电 , the self-discharge mode is negative chemical self-discharge.

[0070] Based on the same inventive concept, the present application also provides a lithium-ion battery, which calculates the self-discharge current and analyzes the cause of self-discharge through the above-mentioned method for detecting the self-discharge of a lithium-ion battery.

[0071] The present invention provides a method, device, and battery for detecting the self-discharge of a lithium-ion battery, which can significantly improve the detection efficiency, and at the same time can determine the cause of self-discharge, providing an important basis for the grading classification and R & D improvement of the battery.

[0072] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for detecting self-discharge of a lithium-ion battery, characterized in that: The method comprises the following steps: Measure the voltage drop and capacity loss of the battery during rest time; It is approximated by the open circuit voltage-capacity curve of the circuit during constant current charge and discharge The ratio of voltage drop to static time is obtained by K value method Estimate the self-discharge current of the positive electrode and the negative electrode; wherein, the self-discharge current of the positive electrode and the negative electrode is estimated by the following formula: Compare the self-discharge currents of the positive and negative electrodes to determine the cause of self-discharge.

2. The method for detecting self-discharge of a lithium-ion battery according to claim 1, characterized in that: The self-discharge current and voltage drop were obtained using a reference electrode.

3. The method for detecting self-discharge of a lithium-ion battery according to claim 1, characterized in that: The self-discharge current and voltage drop are obtained by differential voltage analysis.

4. The method for detecting self-discharge of a lithium-ion battery according to claim 2 or 3, characterized in that: The causes of the self-discharge include internal physical short circuit or positive / negative electrode chemical self-discharge.

5. The method for detecting self-discharge of a lithium-ion battery according to claim 4, characterized in that: Compare the self-discharge currents of the positive and negative electrodes to determine the causes of self-discharge, including: when I 正极自放电 ≈I 负极自放电 , then the self-discharge mode is physical self-discharge; when I 正极自放电 >I 负极自放电 , then the self-discharge mode is positive electrode chemical self-discharge; when I 正极自放电 负极自放电 , then the self-discharge mode is negative electrode chemical self-discharge.​ 6. A testing device, characterized in that: Used to test the causes of self-discharge of lithium-ion batteries, this device includes: A voltage measuring unit, used to measure the open circuit voltage of the battery; A capacity measurement unit for measuring the capacity loss of the battery; A time control unit, used to control the rest time of the battery; The data processing unit is used to approximate the open circuit voltage-capacity curve of the circuit during constant current charging and discharging. The ratio of voltage drop to static time is obtained by K value method Estimate the self-discharge current of the positive electrode and the negative electrode; wherein, the self-discharge current of the positive electrode and the negative electrode is estimated by the following formula: Compare the self-discharge currents of the positive and negative electrodes to determine the cause of self-discharge.

7. The testing device according to claim 6, characterized in that: The data processing unit obtains the self-discharge current and voltage drop through a reference electrode or a differential voltage method.

8. The testing device according to claim 7, characterized in that: The data processing unit compares the self-discharge currents of the positive and negative electrodes to determine the cause of the self-discharge, including: when I 正极自放电 ≈I 负极自放电 , then the self-discharge mode is physical self-discharge; when I 正极自放电 >I 负极自放电 , then the self-discharge mode is positive electrode chemical self-discharge; when I 正极自放电 负极自放电 , then the self-discharge mode is negative electrode chemical self-discharge.​ 9. A lithium ion battery, characterized in that: include: The self-discharge current is calculated and the cause of the self-discharge is analyzed by the lithium-ion battery self-discharge detection method according to any one of claims 1 to 5.

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