CN111136033A

CN111136033A - Screening method for consistency of lithium ion batteries

Info

Publication number: CN111136033A
Application number: CN202010015854.2A
Authority: CN
Inventors: 殷现国; 李涛; 周会
Original assignee: Shandong Jinggong Power Technology Co Ltd
Current assignee: Shandong Jinggong Power Technology Co Ltd
Priority date: 2020-01-08
Filing date: 2020-01-08
Publication date: 2020-05-12

Abstract

The invention discloses a screening method for lithium ion battery consistency, which is characterized by being carried out in a static and dynamic combined mode. The battery core with the first formation and grading capacity is placed at a high temperature and then static voltage and internal resistance are screened, in the grading process again, after capacity and constant current ratio are screened based on charge and discharge data, the charge and discharge capacity is normalized to correspond to different charge and discharge SOC states, and voltages in different SOC states are screened, so that the consistency of dynamic voltage of the battery in the charge and discharge process can be effectively improved. The uniformity of the whole battery is improved through the uniformity of static self-discharge and the uniformity of dynamic voltage change.

Description

Screening method for consistency of lithium ion batteries

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a lithium ion battery consistency screening method.

Background

The nobel chemical prize evaluation committee has pointed out in the awards that light, rechargeable and powerful lithium ion batteries have been applied to various products such as mobile phones, notebook computers, electric vehicles and the like on a global scale, and can store a large amount of energy from solar energy and wind energy, thereby enabling a fossil-fuel-free society. As seen in the royal science academy in sweden, today's lithium ion batteries are not only a high and new research result, but are also part of the world where we are familiar, and even a huge industry. The current technical development of lithium batteries has been mainly to control the cost, improve the energy density and power density of lithium batteries, enhance the safety of use, prolong the service life, and improve the consistency of grouping, and the improvement of these factors still remains the biggest challenge faced by lithium batteries. The uniformity of the single batteries refers to the degree of uniformity of various performances of each electric core forming the battery pack, the non-uniformity of the single batteries is an important influence factor of the performance of the battery pack, the available capacity of the battery pack can be reduced, and the cycle life of the battery pack is shortened, so that the search for an effective method for screening the uniformity of the batteries is urgently expected by a plurality of lithium battery enterprises at present.

Disclosure of Invention

The invention provides a method for screening consistency of lithium ion batteries, which solves the problems of large battery pressure difference and poor consistency in battery matching so as to improve the available capacity and cycle life of a battery pack.

A screening method for lithium ion battery consistency is characterized by comprising the following specific screening steps:

step 1, after the battery to be detected after being formed into the partial capacity is placed at the same high temperature, measuring voltage and internal resistance, and screening according to the voltage standard of 3-5 mV and the internal resistance standard of 2-3 m omega;

step 2: charging and discharging the batteries screened in the step 1, and screening the battery capacity according to the capacity standard based on the charging and discharging data;

and step 3: screening the batteries screened in the step 2 according to a formula that K is constant current charging capacity/total charging capacity, wherein K is a constant current ratio;

and 4, step 4: calculating the charge and discharge state of the battery screened in the step 3 through a formula of 'charge and discharge state = (charge and discharge capacity/total capacity) × 100%', so as to finish the normalization processing of the charge and discharge capacity of the battery;

and 5: the batteries were screened according to the voltage difference standards in the charge and discharge states of 0%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, and 100%.

Preferably, in the step 5, the standard for the 0%, 5%, 10% charge/discharge state voltage difference is 25mV, the standard for the 20%, 30%, 40%, 50%, 60%, 70%, 80% charge/discharge state voltage difference is 15mV, and the standard for the 90%, 95%, 100% charge/discharge state voltage difference is 25 mV.

Preferably, the standing temperature in the step 1 is 45-50 ℃, and the standing time is 7 days.

Preferably, the capacity standard in the step 2 is 20-40 mAh.

Preferably, the constant current ratio standard in the step 3 is 0.5%.

The beneficial effect of this application does:

the high-temperature shelving accelerates the self-discharge process, and is beneficial to screening the consistency of self-discharge;

1. in the secondary capacity grading process, the constant current ratio is limited, so that the screening of the lithium ion migration rate consistency in the battery is facilitated;

2. through the normalization processing of the capacity, the pressure difference of different charging and discharging states is controlled, and the screening of the consistency of the dynamic pressure difference is facilitated;

after the batteries are screened by the method, the consistency of the batteries can be effectively improved, so that the service life of the battery pack is prolonged.

Detailed Description

The present application is further illustrated by the following examples of specific embodiments.

Example 1

Taking the screening of 18650 lithium iron phosphate cylindrical batteries as an example, the specific steps are as follows

1. Standing the battery cell with the charge capacity of 50% at 50 ℃ for 7 days, and performing primary screening by using a voltage standard of 3mV and an internal resistance standard of 3m omega;

2. carrying out 1C charge-discharge test on the battery, and screening according to the capacity standard of 25 mAh;

3. the battery constant current ratio K is screened, the standard is 0.5%, and the calculation formula of the battery constant current ratio K is that K is constant current charging capacity/total charging capacity.

4. The charge and discharge capacities were normalized to correspond to different charge and discharge states, "charge and discharge state = (charge and discharge capacity/total capacity) × 100%", as shown in tables 1, 2, and 3;

5. the charge and discharge states are respectively screened to be corresponding voltages of 0%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% and 100%, the standard of the voltage difference of 0% to 10% of the charge and discharge states is 25mV, the standard of the voltage difference of 11% to 89% of the charge and discharge states is 15mV, and the standard of the voltage difference of 90% to 100% of the charge and discharge states is 25 mV. According to the accumulation of a large amount of data in the previous period, the distribution ranges of the corresponding voltages of a large number of batteries in different charging and discharging states are analyzed, and specific upper limit control voltage and lower limit control voltage are formulated by combining a voltage difference standard, as shown in table 4. Comparing 1#, 2#, 3# batteries, wherein only 1# and 2# batteries accord with the voltage screening standard in table 4, and other batteries continue to be classified by expanding the screening standard.

Table 1186501 # battery charge-discharge capacity normalization processing data table

TABLE 2186502 normalized processing table for battery capacity

TABLE 3186503 normalized processing table for battery capacity

TABLE 4 Voltage screening standards (class A) for different charging and discharging states

Example 2

Taking the screening of the consistency of 26650 lithium iron phosphate cylindrical batteries as an example, the specific steps are as follows

1. Standing the battery cell with the charge quantity of 50% at 50 ℃ for 7 days after formation and capacity grading, and performing primary screening by using the voltage and internal resistance standard of 3mV and 3m omega;

2. performing 0.5C charge and discharge test on the battery, and screening according to the capacity standard of 40 mAh;

3. screening the constant current ratio K of the battery with the standard of 0.5%;

4. performing normalization processing on the charge and discharge capacity to enable the charge and discharge capacity to correspond to different charge and discharge states, wherein the charge and discharge state = (charge and discharge capacity/total capacity) × 100% "; as shown in tables 5, 6 and 7;

5. screening voltages corresponding to charge and discharge states of 0%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% and 100%, respectively, wherein the standard of the voltage difference between 0% and 10% of the charge and discharge states is 25mV, the standard of the voltage difference between 11% and 89% of the charge and discharge states is 15mV, and the standard of the voltage difference between 90% and 100% of the charge and discharge states is 25mV, analyzing corresponding voltage distribution ranges of a large number of batteries in different charge and discharge states according to a large amount of data accumulation in the previous period, and establishing specific upper limit control voltage and lower limit control voltage by combining the voltage difference standards, as shown in Table 8. For comparison with 1#, 2#, 3# batteries, 3 batteries all met the voltage screening standard in table 8.

TABLE 5266501 normalized processing table for battery capacity

TABLE 6266502 normalized processing table for battery capacity

TABLE 7266503 normalized processing table for battery capacity

TABLE 8 Voltage screening standards (class A) for different charging and discharging states

Claims

1. A screening method for lithium ion battery consistency is characterized by comprising the following specific screening steps:

2. The method according to claim 1, wherein in step 5, the standard for the voltage difference between 0%, 5% and 10% of the charge/discharge states is 25mV, the standard for the voltage difference between 20%, 30%, 40%, 50%, 60%, 70% and 80% of the charge/discharge states is 15mV, and the standard for the voltage difference between 90%, 95% and 100% of the charge/discharge states is 25 mV.

3. The screening method for lithium ion battery consistency according to claim 1, wherein the resting temperature in the step 1 is 45-50 ℃ and the resting time is 7 days.

4. The screening method for lithium ion battery consistency according to claim 1, wherein the capacity standard in the step 2 is 20-40 mAh.

5. The method for screening lithium ion battery consistency according to claim 1, wherein the constant current ratio standard in the step 3 is 0.5%.