CN102901931A - Method for screening lithium battery with abnormal self-discharge - Google Patents

Abstract

The invention discloses a method for screening lithium batteries with abnormal self-discharge, which specifically comprises the following steps: fully charging the lithium battery, and standing in parallel; measuring the current between adjacent lithium batteries by using an ammeter; and calculating the net inflow current of each lithium battery, and judging whether the self-discharge is abnormal or not by using the magnitude of the net inflow current of the batteries. The invention picks out the batteries with overlarge self-discharge before grouping by a simple and rapid method, thereby avoiding the influence on the consistency of the whole group of batteries, improving the performance of the battery pack and prolonging the service life of the batteries.

Description

Method for screening lithium batteries with abnormal self-discharge

technical field

The invention relates to the technical field of lithium ion batteries, in particular to a method for screening lithium batteries with abnormal self-discharge.

Background technique

When there is no external discharge circuit for storage batteries and primary batteries, the terminal voltage will decrease and the available power will be lost, which is called self-discharge. Due to the influence of raw materials and manufacturing processes, the self-discharge rate of a small amount of lithium-ion batteries will reach several times that of normal batteries. These batteries are used in series and parallel with other batteries, which will seriously affect the performance of the entire battery pack. It is necessary to select batteries with excessive self-discharge rate and treat them as substandard products.

The detection of self-discharge rate, according to the national standard, needs more than 30 days, which brings great inconvenience to the operation. Patent CN201110388882.X discloses a method for accelerating the self-discharge rate by using a magnetic field. Use 0.33C at room temperature to fully charge the battery to be selected, then place it in a magnetic field generator, adjust the ambient temperature to 45 to 55 degrees Celsius, place it for 1 to 15 days, take it out, degauss, add electricity at room temperature, and fill in the capacity to account for the full capacity The percentage is taken as the self-discharge rate. Although this method can shorten the test time by more than half, the magnetic field and the continuous high temperature environment need to pay a high cost. Patent 201110031739.5 proposes a method. Fully charge the battery with constant current and constant voltage at room temperature, record C1, place it for 1 to 6 days, then fully charge it in the same way, record C2, and judge the battery by the ratio of C2 and C1. The size of the self-discharge rate. This method, under the same conditions, shortens the standard time from 28 days to 1 to 6 days. Although there is no pressure on the environment and test costs, the test accuracy is greatly reduced. The shorter the time, the higher the reliability. Low. Therefore, it is necessary to invent a simple and fast screening method for battery self-discharge, which can solve the problems caused by test time, test environment, test cost, etc., and keep the test results reliable.

Contents of the invention

The object of the present invention is to provide a method for screening lithium batteries with abnormal self-discharge. The present invention can simply and conveniently select lithium batteries with excessive self-discharge without requiring too long time, special environment and too high the cost of.

The technical scheme adopted in the present invention is:

A method for screening lithium batteries with abnormal self-discharge, characterized in that it specifically comprises the following steps:

1) First, fully charge the lithium battery to be tested, group the lithium batteries, the number of lithium batteries in each lithium battery group is m, and the m lithium batteries of the same lithium battery group are connected in parallel with each other, and the lithium batteries after parallel connection Set aside in a stable environment for 30-50 hours;

2) Disconnect the parallel connection between two adjacent lithium batteries (nth and n+1th lithium batteries), keep the parallel connection between other batteries, and use an ammeter to measure the current flowing from nth to n+1th lithium battery , and recorded as I _an , the values of n are 1, 2, 3...m, where I _a0 =I _am =0;

3) Calculate the net inflow current I _n = I _a(n-1) -I _an of each lithium battery in the lithium battery pack, and the value of n is 1, 2, 3...m;

4) The higher the self-discharge rate of lithium batteries with higher net inflow current, the abnormal current value I is determined according to the relevant requirements for self-discharge screening of lithium batteries and the distribution of net inflow current values of m lithium batteries;

5) Among each lithium battery, the lithium battery with a net inflow current I _n higher than the abnormal current value I is a lithium battery with abnormal self-discharge;

6) Pick out the lithium battery with abnormal self-discharge from the lithium battery pack.

The parallel connection between the lithium batteries is a detachable movable connection.

The range of the ammeter matches the maximum measured current value of the lithium battery to be tested.

Principle of the present invention is:

The self-discharge current of the lithium battery is related to the monthly self-discharge rate. The calculation method is as follows: if the monthly self-discharge rate of the lithium battery is x%, and the capacity of the lithium battery is C, then the theoretical self-discharge current Ix=x%×C/ (28×24).

When calculating or selecting the net inflow current and abnormal current value of the lithium battery, the self-discharge current Ix calculated by the above formula can be used as the basis for the self-discharge rate of normal and abnormal lithium batteries.

In the method for judging self-discharge abnormality by measuring current in parallel in the present invention, since the batteries are connected in parallel and are quasi-static, it can be considered that the SOC of all batteries in the group is consistent, and the sum of the self-discharge and external discharge currents of each battery should be equal. Therefore, it is possible to measure and calculate the net inflow current of each lithium battery to judge the self-discharge of the lithium battery.

The advantages of the present invention are:

By measuring the net inflow current of the parallel batteries, the invention can simply and conveniently pick out the batteries with excessive self-discharge before they are grouped, so as to avoid affecting the consistency of the whole group of batteries, improve the performance of the battery group, and prolong the battery life.

Description of drawings

Figure 1 is a connection diagram for measuring the current between batteries after the batteries are connected in parallel and balanced

1 is the ammeter, 2 is the switch, 3 is the battery to be tested

Detailed ways

Specific implementation mode 1

Pick out the batteries with abnormal self-discharge rate from the 3.2V10Ah batteries that are ready to be assembled into 300V50Ah electric vehicles.

A method for screening lithium batteries with abnormal self-discharge, specifically comprising the following steps:

At first the lithium battery 3 to be tested is fully charged, and 100 lithium batteries 3 of every group are connected in parallel, and stand for 40 hours in the workshop; The self-discharge rate of abnormal self-discharge batteries is greater than 12%, and the self-discharge current of abnormal batteries is 1.79mA; select mA meter 1 (range 2mA, accuracy 0.001mA) to connect with wire 2 and measure the current between adjacent lithium batteries Current, calculate the net inflow current of each lithium battery; if the normal rate is 90%, the average self-discharge current is 0.74×0.9+1.79×0.1=0.85mA. The net inflow current of a normal battery with a monthly self-discharge rate of 5% is 0.74-0.85=-0.11mA, while the net inflow current of a battery with an abnormal monthly self-discharge rate (12%) is 1.79-0.85=0.95 mA. Therefore, batteries with a net inflow current value greater than 0.9 mA were picked out as batteries with abnormal self-discharge.

Claims (3)

1. A method for screening a lithium battery with abnormal self-discharge, characterized in that, specifically comprising the following steps: (1) First, fully charge the lithium battery to be tested, and group the lithium batteries. The number of lithium batteries in each lithium battery group is m, and the m lithium batteries in the same lithium battery group are connected in parallel with each other. The lithium batteries after parallel connection The battery pack is placed in a stable environment for 30-50 hours; (2) Disconnect the parallel connection between two adjacent lithium batteries, keep the parallel connection between other batteries, use an ammeter to measure the current flowing from n cells to n+1 lithium cells, and record them as I _an and n respectively The value is 1,2,3...m, where I _a0 =I _am =0; (3) Calculate the net inflow current of each lithium battery in the lithium battery pack = I _a(n-1) -I _an , where the value of n is 1, 2, 3...m; (4) The larger the net inflow current of the lithium battery, the higher the self-discharge rate. According to the requirements for the self-discharge of the lithium battery or the distribution of the net inflow current values of m lithium batteries, determine the value of the abnormal current I; (5) Among each lithium battery, the lithium battery with a net inflow current I _n higher than the abnormal current I is a lithium battery with abnormal self-discharge; (6) Pick out the lithium battery with abnormal self-discharge from the lithium battery pack. 2. The screening method for lithium battery self-discharge according to claim 1, characterized in that: the parallel connection between the lithium batteries is a detachable movable connection. 3. The screening method for lithium battery self-discharge according to claim 1, characterized in that: the range of the ammeter matches the maximum measured current value of the measured lithium battery.

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