CN106154173A - Quick, cheap and convenient self-discharge screening method for secondary battery - Google Patents

Abstract

The invention relates to a fast, cheap and convenient self-discharge screening method for secondary batteries, which includes the following steps: (1) In the constant voltage charging section of the battery capacity test charging, count the current value or a certain current value of the battery under test at a certain moment The constant voltage charging time under the current value; (2) Determine the standard current value range of the normal battery at the same time as the tested battery at the constant voltage charging stage or the constant voltage charging time range under the same current value; (3) The tested battery Compare the current value or constant voltage charging time with the normal battery current value or constant voltage charging time, if the measured current value exceeds the standard current value range or the constant voltage charging time of the tested battery exceeds the constant voltage charging time range of the normal battery, Then it is judged that the battery is a self-discharging abnormal battery, otherwise, it is a normal battery. The method of the invention greatly shortens the screening time of the secondary battery at the factory, effectively improves the self-discharge consistency of the battery, and prolongs the service life of the battery pack.

Description

A fast, cheap and convenient self-discharge screening method for secondary batteries

technical field

The invention belongs to the technical field of battery detection, and in particular relates to a fast, cheap and convenient self-discharge screening method for secondary batteries.

Background technique

Secondary batteries, especially lithium-ion batteries, have become increasingly popular. Especially in the past two years, with the rapid development of new energy vehicles, the demand for lithium-ion power batteries has also grown vigorously. Regardless of whether it is a single battery or a series-parallel battery pack (system), the screening of self-discharge is an essential step before leaving the factory, especially for battery systems, the consistency of self-discharge largely determines the quality of the battery system. In addition, the after-sales problems of some zero-voltage batteries also point to the over-discharge caused by serious self-discharge batteries. The consistency of self-discharge has become an important criterion for battery consistency evaluation in addition to capacity and internal resistance. one.

At present, the self-discharge screening methods for secondary batteries, especially lithium-ion batteries, can be roughly divided into two categories: one is to use precision testing equipment to directly detect the size of the internal self-discharge current of the battery through certain methods and means, so as to calculate the self-discharge of the battery. Discharge rate, this method is fast and simple, but it requires high equipment accuracy, and it cannot meet the needs of industrialization at present; the other is to use the time accumulation method to count the change of the open circuit voltage of the battery within a certain period of time at a certain temperature Or capacity attenuation to establish battery self-discharge evaluation criteria. No matter how this method is improved, it cannot get rid of the problem that it takes a certain amount of time to shelve, which greatly prolongs the delivery time of battery products. Although high temperature shelving can greatly shorten The time for self-discharge screening, but the site and temperature control requirements of the high-temperature aging room undoubtedly add a higher cost to the battery cell.

Contents of the invention

The purpose of the present invention is to provide a fast, cheap and convenient self-discharge screening method for secondary batteries, which can effectively prevent batteries with large self-discharge from flowing into the next process. In addition, by establishing self-discharge sorting standards, the consistency of batteries Huge improvements.

To achieve the above object, the present invention adopts the following technical solutions:

A fast, cheap and convenient self-discharge screening method for secondary batteries, comprising the following steps:

(1) During the charging process of the battery capacity test, test the current value corresponding to different moments in the constant voltage charging stage of the battery, and count the current value of the battery under test at a certain moment or the constant voltage charging time under a certain current value;

(2) According to the type and production batch of the battery under test, determine the standard current value range of the normal battery at the same time as the battery under test at the constant voltage charging stage or the constant voltage charging time range at the same current value;

(3) Compare the current value or constant voltage charging time of the battery under test with the current value or constant voltage charging time of the normal battery, if the measured current value exceeds the standard current value range or the constant voltage charging time of the battery under test exceeds the normal The constant voltage charging time range of the battery is determined to be a battery with abnormal self-discharge, otherwise, it is a normal battery.

In step (1), the current value of the battery under test at a certain moment refers to the current value of different batteries under test at the same time when the constant voltage charging starts during the constant voltage charging process. The constant-voltage charging time at a certain current value refers to the time required to reach the specified current at the beginning of the constant-voltage charging stage during the constant-current and constant-voltage charging process.

In step (3), if the measured current value exceeds the standard current value range or the constant voltage charging time of the tested battery exceeds the constant voltage charging time range of the normal battery, the greater the battery self-discharge rate is.

It can be seen from the above technical solution that the fast, cheap and convenient self-discharge screening method for secondary batteries described in the present invention uses the battery capacity to test the current value at a certain moment in the constant voltage charging stage of the charging process or the current value at a certain current value. Constant voltage charging time to quickly determine the size of the battery self-discharge rate, effectively making up for the shortcomings of the current two types of self-discharge screening methods, reducing the cost of secondary battery self-discharge screening, and greatly shortening the secondary battery factory screening time , effectively improving the consistency of battery self-discharge and prolonging the service life of the battery pack.

Description of drawings

Fig. 1 is the current-time curve diagram of the constant voltage charging section of the normal two batteries of the discharge of the present invention;

Fig. 2 is the current-time graph of the constant voltage charging section of two batteries with abnormal self-discharge but different self-discharge rates according to the present invention.

detailed description

The present invention will be further described below in conjunction with accompanying drawing:

A fast, cheap and convenient self-discharge screening method for secondary batteries, comprising the following steps:

S1: During the charging process of the battery capacity test, test the current value corresponding to different moments in the constant voltage charging stage of the battery, and count the current value of the battery under test at a certain moment or the constant voltage charging time under a certain current value;

In this step, the current value of the battery under test at a certain moment refers to the current value of different batteries under test at the same time when the constant voltage charging starts during the constant voltage charging process. The constant-voltage charging time at a certain current value refers to the time required to reach the specified current at the beginning of the constant-voltage charging stage during the constant-current and constant-voltage charging process.

For example: count the charging current values of different tested batteries based on the same time T (this time needs to be counted from the start of constant voltage charging), or use the same current value I as a benchmark to count the charging current values of different tested batteries under this current value required charging time.

S2: According to the type and production batch of the battery under test, determine the standard current value range of the normal battery at the same time as the battery under test at the constant voltage charging stage or the constant voltage charging time range at the same current value;

S3: Compare the current value or constant voltage charging time of the tested battery with the current value or constant voltage charging time of the normal battery, if the measured current value exceeds the standard current value range or the constant voltage charging time of the tested battery exceeds the normal battery If the constant voltage charging time range is within the range, it is judged that the battery is an abnormal self-discharge battery, otherwise, it is a normal battery.

For example: define the current value i range of a normal battery at a certain moment t as a≤i≤b (the values of a and b are defined according to the battery type and production batch), if the current value I of the battery under test exceeds the range of i, Then it can be judged that the battery under test is an abnormal self-discharge battery, and the larger I is, the greater the self-discharge rate of the battery under test.

Similarly, the range of the constant voltage charging time t of a normal battery defined at a certain current i is m≤t≤n (the values of m and n are defined according to the battery type and production batch), if the battery under test is charged at the same current i If the time T below exceeds the normal battery t value range, it can be judged that the battery under test is an abnormal self-discharge battery, and the larger the T value, the greater the battery self-discharge rate.

As shown in Figure 1 and Figure 2, according to the current value of the battery under test at different times, an intuitive judgment can be made by drawing the current-time curve. , and the battery with abnormal self-discharge will have a significant difference (i1>i2 at time t2 in Figure 2). The battery with a higher self-discharge rate will have a larger current value. Of course, in order to make the difference more obvious, the preferred value of t is 600s-1500s; or use the same current value i (this current value should be less than or equal to half of the current value of the constant current charging section) as a benchmark to count the constant voltage charging time value of different batteries (this time needs to start from the constant voltage charging Timing), as shown in Figure 2, t2>t1 under the value of i1, the larger the value of t, the greater the self-discharge rate of the battery.

The constant voltage section in the constant current and constant voltage charging process of the battery is the process of floating charging the battery with a continuously decreasing current. Under normal circumstances, this current will show an exponential function decay trend; however, for a battery with abnormal self-discharge, its internal The self-discharge current of the battery may approach or reach a certain value of the floating charge current. At this time, the constant voltage charging of the battery will last for a long time or even continue, and the above situation will appear in the curve of the constant voltage charging.

The above-mentioned embodiments are only descriptions of preferred implementations of the present invention, and are not intended to limit the scope of the present invention. Variations and improvements should fall within the scope of protection defined by the claims of the present invention.

Claims (4)

1. A fast, cheap and convenient self-discharge screening method for secondary batteries, is characterized in that, comprising the following steps: (1) During the charging process of the battery capacity test, test the current value corresponding to different moments in the constant voltage charging stage of the battery, and count the current value of the battery under test at a certain moment or the constant voltage charging time under a certain current value; (2) According to the type and production batch of the battery under test, determine the standard current value range of the normal battery at the same time as the battery under test at the constant voltage charging stage or the constant voltage charging time range at the same current value; (3) Compare the current value or constant voltage charging time of the battery under test with the current value or constant voltage charging time of the normal battery, if the measured current value exceeds the standard current value range or the constant voltage charging time of the battery under test exceeds the normal The constant voltage charging time range of the battery is determined to be a battery with abnormal self-discharge, otherwise, it is a normal battery. 2. The fast, cheap and convenient self-discharge screening method for secondary batteries according to claim 1, characterized in that in step (1), the current value of the battery under test at a certain moment refers to the current value during the constant voltage charging process Timing at the start of medium-constant-voltage charging, and the current values of different batteries under test at the same moment. 3. The fast, cheap and convenient self-discharge screening method for secondary batteries according to claim 1, characterized in that, in step (1), the constant voltage charging time under a certain current value refers to the charging time at constant current and constant During the voltage charging process, the time required for counting to the specified current at the beginning of the constant voltage charging stage. 4. The fast, cheap and convenient self-discharge screening method for secondary batteries according to claim 1, characterized in that in step (3), if the measured current value exceeds the standard current value range or the constant voltage charging of the tested battery The greater the time range beyond the constant voltage charging time of the normal battery, the greater the self-discharge rate of the battery.