1. A consistency screening method for high-power lithium ion storage batteries is characterized by comprising the following steps:

s1: charging a lithium ion storage battery to be screened to a specified voltage and current;

s2: carrying out high-frequency pulse discharge on the lithium ion storage battery for a specified time through an electronic load;

s3: acquiring the change waveforms of the current and the voltage of the lithium ion storage battery in the step S2 through an oscilloscope;

s4: dividing the peak-to-peak value of the voltage change by the peak-to-peak value of the current change to obtain the equivalent resistance of the lithium ion storage battery;

s5: and (4) repeatedly executing the step (S1) to the step (S4) to complete the calculation of the equivalent resistance of the plurality of lithium ion storage batteries, performing statistical analysis on the equivalent resistance of the plurality of lithium ion storage batteries, and selecting the lithium ion storage batteries with consistency.

2. The method for screening consistency of high-power lithium ion storage batteries according to claim 1, wherein in step S1, the lithium ion storage battery is charged to a specified voltage by a constant current method, and then charged to a specified current by a constant voltage method, and the specified voltage is between 3.9V and 4.1V.

3. The method for screening consistency of high-power lithium-ion storage batteries according to claim 1, wherein the discharging time of the electronic load to the lithium-ion storage batteries in the step S2 is not more than 1 minute.

4. The method for screening consistency of high-power lithium ion storage batteries according to claim 1, wherein the frequency of discharging the lithium ion storage batteries by the electronic load in step S2 is between 1k Hz and 5k Hz.

5. The method for screening consistency of high-power lithium-ion storage batteries according to claim 1, wherein the discharge rate of the electronic load to the lithium-ion storage batteries in the step S2 is 1C-5C.

6. The method for screening consistency of high-power lithium ion storage batteries according to claim 1, wherein in step S5, the statistical analysis method of equivalent resistance of the lithium ion storage batteries is to calculate a standard deviation δ of the equivalent resistance of the lithium ion storage batteries, and select one-time standard deviation δ to three-time standard deviation 3 δ from the lithium ion storage batteries, so as to select the lithium ion storage batteries with consistency.

Background

A lithium ion battery pack (hereinafter referred to as a battery pack) is generally formed by connecting a plurality of lithium ion battery cells (hereinafter referred to as battery cells) in series and in parallel, and the service life of the battery pack is generally limited by the worst-performance battery cell in the battery pack, so that the consistency of the battery cells in the battery pack has an important influence on the performance of the battery pack. The screening of the storage battery monomer which forms the storage battery pack at present mainly comprises static screening and dynamic screening, wherein the static screening is realized by matching parameters such as internal resistance, open-circuit voltage and capacity of the storage battery monomer. The dynamic screening is to discharge the storage battery monomer according to the specified working condition, and the screening is carried out by matching the discharge curve. The equivalent model of the lithium ion storage battery comprises a resistance element and a capacitance element, the screening method can only reflect the resistance characteristic, and the capacitance characteristic has important significance for the high-power lithium ion storage battery.

Therefore, it is necessary to provide a method capable of screening out high-power lithium ion batteries with better consistency more quickly and reflecting the characteristics of the high-power lithium ion batteries more accurately.

Disclosure of Invention

The invention aims to provide a consistency screening method of a high-power lithium ion storage battery, which can realize quick and accurate screening of the lithium ion storage battery and can also take resistance characteristics and capacitance characteristics of the lithium ion battery into consideration.

In order to achieve the purpose, the invention provides a consistency screening method of a high-power lithium ion storage battery, which comprises the following steps:

s1: charging a lithium ion storage battery to be screened to a specified voltage and current;

s2: carrying out high-frequency pulse discharge on the lithium ion storage battery for a specified time through an electronic load;

s3: acquiring the change waveforms of the current and the voltage of the lithium ion storage battery in the step S2 through an oscilloscope;

s4: dividing the peak-to-peak value of the voltage change by the peak-to-peak value of the current change to obtain the equivalent resistance of the lithium ion storage battery;

s5: and repeating the steps S1 to S4 to complete the calculation of the equivalent resistance of the plurality of lithium ion storage batteries, and performing statistical analysis on the equivalent resistance of the plurality of lithium ion storage batteries to select the lithium ion storage batteries with consistency.

Preferably, in step S1, the lithium ion battery is charged to a predetermined voltage by a constant current method, and then charged to a predetermined current by a constant voltage method, wherein the predetermined voltage is between 3.9V and 4.1V.

Preferably, the discharging time of the lithium ion storage batteries by the electronic load in the step S2 is not more than 1 minute.

Preferably, the frequency of discharging the lithium ion storage batteries by the electronic load in the step S2 is between 1kHz and 4 kHz.

Preferably, the rate of discharge of the lithium ion secondary batteries by the electronic load in step S2 is 1C to 5C.

Preferably, in the step S5, the statistical analysis method for the equivalent resistance of the lithium ion batteries is to calculate a standard deviation δ of the equivalent resistance of the lithium ion batteries, and select one-time standard deviation δ to three-time standard deviation 3 δ from the lithium ion batteries, so as to select a consistent lithium ion battery.

The consistency screening method for the high-power lithium ion storage battery provided by the invention has the beneficial effects that:

the high-frequency large-current pulse discharge is carried out on the lithium ion storage battery, the equivalent resistance is obtained by calculating the voltage fluctuation condition and the current fluctuation condition to screen the lithium ion storage battery, meanwhile, the resistance characteristic and the capacitance characteristic inside the lithium ion storage battery are screened, the dynamic characteristic and the power characteristic inside the storage battery are accurately reflected, the screening method is rapid and accurate, and the monomer consistency is improved.

Drawings

FIG. 1 is a flow chart of a screening method of the present invention;

FIG. 2 is a cell voltage curve during the discharge of a lithium ion battery cell screened by the present invention.

Detailed Description

The consistency screening method for the high-power lithium ion storage battery provided by the invention is further described in detail below with reference to the accompanying drawings and the detailed description. The advantages and features of the present invention will become more apparent from the following description.

As shown in fig. 1, the consistency screening method for the high-power lithium ion storage battery provided by the invention comprises the following steps:

step 1, taking a 30Ah lithium ion storage battery as an example of a single body, continuously charging the 30Ah lithium ion storage battery at a current of 6A until the voltage of the 30Ah lithium ion storage battery reaches 4.0V at normal temperature (20 ℃), and continuously charging the 30Ah lithium ion storage battery at a constant voltage (keeping the voltage of the storage battery at 4.0V) until the charging current is less than 1.5A.

And 2, carrying out pulse discharge on the charged 30Ah lithium ion storage battery in the step 1 for 1 minute at the frequency of 3k Hz and the current of 60A through an electronic load.

And 3, adopting an oscilloscope to monitor the current and voltage change conditions of the lithium ion storage battery in the process of the step 2 in real time.

And 4, according to the collected monitoring data in the figure 2, the current fluctuation value of the 30Ah lithium ion storage battery under the electronic load loading is 78A, the voltage fluctuation value is 266mV, and the equivalent resistance of the 30Ah lithium ion storage battery is calculated to be 3.4m omega according to the values.

Step 5, repeatedly executing steps S1 to S4, and calculating equivalent resistances of a plurality of lithium ion storage batteries of the same type (in this embodiment, all of the lithium ion storage batteries of 30Ah are calculated); and calculating the standard deviation delta of the equivalent resistance of the 30Ah lithium ion storage batteries by adopting a statistical analysis method according to the equivalent resistance calculated by the 30Ah lithium ion storage batteries of each monomer, and selecting the lithium ion storage battery monomers within the range of 1 delta for assembly. Fig. 2 shows the voltage conditions of the 11-cell series lithium ion battery pack obtained by screening by the method in the discharge processes of 6A and 150A, and it can be seen that the voltage uniformity of each cell in the battery pack is excellent.

While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.