CN110813799A

CN110813799A - Consistency screening method of lithium titanate single battery for high rate

Info

Publication number: CN110813799A
Application number: CN201810915676.1A
Authority: CN
Inventors: 高雅; 陈啸天; 钱丽; 吴可
Original assignee: CITIC Guoan Mengguli Power Technology Co Ltd
Current assignee: RiseSun MGL New Energy Technology Co Ltd
Priority date: 2018-08-13
Filing date: 2018-08-13
Publication date: 2020-02-21

Abstract

The invention relates to a consistency screening method of a lithium titanate single battery for high rate, and the screened lithium titanate battery has high consistency under a large-current discharge working condition. The method comprises the following steps: the battery is adjusted to a specific charge state and is placed at a high temperature for a short time, so that the battery with large self-discharge can be rapidly screened; and then, carrying out high-frequency and low-frequency alternating current impedance test of a specific single point on the battery after the battery is placed at a high temperature, and visually reflecting the ohmic internal resistance and the polarization internal resistance of the battery. The method disclosed by the invention can be used for rapidly and accurately evaluating the self-discharge and dynamic internal resistance of the battery while considering the parameters of conventional discharge capacity, open-circuit voltage, constant voltage time, static internal resistance and the like, so that the screening result is more comprehensive, accurate and effective; and the scheme can realize the screening of the consistency of the batteries within 1 day, can greatly shorten the screening period of the batteries, is simple and convenient to operate, has low energy consumption, and is suitable for large-scale batch application of an automatic production line.

Description

Consistency screening method of lithium titanate single battery for high rate

Technical Field

The invention belongs to the technical field of battery detection, and relates to a consistency screening method of a lithium titanate single battery for high rate.

Background

The unique high safety, excellent large-current charge and discharge performance, ultra-long service life and low-temperature characteristics of the lithium titanate battery become the priority of the power supply of the fast-charging lithium ion power battery, the rail transit vehicle-mounted lithium battery and the start-stop system. In practical application, the lithium titanate battery needs to be used in a series-parallel battery pack, the charging and discharging working condition can reach about 10 ℃, and the requirement of the series-parallel mode on the consistency among the single batteries is extremely strict. Therefore, the lithium titanate batteries with higher consistency can be quickly, effectively and accurately screened out, the service life and the safety of the whole power system under the condition of high-rate working condition and the energy efficiency during starting/braking can be improved, and the application market of the lithium titanate batteries can be widened.

The battery consistency screening needs to comprehensively consider a plurality of parameters such as discharge capacity, platform voltage, open-circuit voltage, battery internal resistance and self-discharge of the single battery, but the existing screening method has less parameter setting and has lower accuracy and precision of screening results. In addition, for testing specific parameters such as self-discharge and polarization internal resistance, the existing method (for example, commonly used HPPC method for testing polarization internal resistance) is long in time consumption, large in energy consumption, complex in operation, and requires large-current pulse charging and discharging equipment, so that the method is not suitable for industrial popularization and application. For example, the Chinese patent application No. 201710818877.5 discharges the battery to 1.3-1.8V (about 46-64%_SOC) The high temperature shelf is carried out in the range, and the self-discharge over-large battery is screened by the method of testing the open circuit voltage difference before and after the shelf, but the screening time used in the application is still longer in the selected voltage range, about 1-2 days, and the method does not consider the difference of the polarization internal resistance of the battery. The chinese patent application No. 201710773164.1 considers static parameters, direct current internal resistance, self-discharge and other dynamic parameters, but the method must perform 10-20C high-rate pulse discharge on the battery, and taking example 1 thereof, the method needs to perform pulse charge and discharge with 250A current, which not only requires high-rate pulse charge and discharge equipment, higher equipment investment and large energy consumption, but also may cause damage to the battery itself leaving factory, and the operability is not strong, and the method prefers a high-temperature shelf time of 7-10 days, and has long time, and needs to perform a complicated calculation process, and the screening efficiency is low. The chinese patent application No. 201710846568.9 screens batteries by multiple times of vibration high-temperature shelving and multiple times of direct current internal resistance tests, and has the disadvantages of large discharge current (maximum current during vehicle operation), complex screening process and long time. Chinese patent application No. 201710824747.2 for testing ac resistance of multiple batteries at multiple different preset ac frequenciesThe method can realize quick matching, but the method is difficult to screen out the batteries with large self-discharge.

Disclosure of Invention

In order to solve the problems, the invention provides a screening method capable of meeting the consistency of a lithium titanate single battery for high multiplying power through analysis and research of a large amount of experimental data. The method is simple and convenient and has extremely high efficiency.

The invention provides a battery consistency screening method, which comprehensively considers a plurality of parameters such as battery discharge capacity, open-circuit voltage, constant voltage time, self-discharge and battery internal resistance, and the like, has more comprehensive and accurate screening results, and for testing the self-discharge and battery polarization internal resistance, the method emphasizes to select a test section which more prominently displays the change of each parameter of a battery and an equivalent substitution mode according to the characteristics of a lithium titanate battery through test and research, does not need heavy current charge and discharge equipment, has simple and convenient operation and short time consumption, and can realize all effects of various complicated screening methods in the prior art on consistency requirements.

The invention provides a screening method for consistency of a lithium titanate single battery for high rate, which specifically comprises the following steps:

step 1: firstly, charging and discharging a battery to be sorted, recording the discharge capacity D of the battery and constant voltage charging time CV-T, then charging the battery to a specific State of Charge (SOC), and measuring the open-circuit voltage OCV1 of the battery at the moment;

step 2: standing the battery obtained in the step 1 in a high-temperature T1 environment for a certain time T1, taking out the battery, cooling the battery to room temperature, and measuring the open-circuit voltage OCV2, the high-frequency alternating internal resistance Rh and the low-frequency alternating internal resistance Rl of the battery at the moment;

and step 3: and comparing the discharge capacity D, the constant-voltage charging time CV-T, the open-circuit voltage OCV1, the voltage drop (OCV2-OCV1), the open-circuit voltage OCV2, the high-frequency alternating internal resistance Rh and the low-frequency alternating internal resistance Rl of the battery to be sorted to quickly sort out the lithium titanate battery which has better consistency and can be charged and discharged under the large-current working condition for use.

Preferably, the number of charging and discharging in step 1 is at least 3, the charging is performed to a voltage corresponding to the specific state of charge SOC by a constant current-constant voltage charging method, and the specific state of charge SOC ranges from 5% to 30%, preferably from 10% to 20%.

Preferably, the range of the high temperature T1 in the step 2 is 45-65 ℃, and the high-temperature shelf time T1 is 5-15 h. The high-temperature T1 is preferably 45-55 ℃, and the high-temperature standing time T1 is preferably 8-12 h;

preferably, the high-frequency alternating internal resistance Rh in step 2 is measured by using a battery impedance meter with a frequency of 1 kHz. And measuring the low-frequency alternating-current internal resistance Rl by using a low-frequency battery impedance instrument with the frequency of 1-2 Hz.

Preferably, in step 3, the conditions for comparison and screening are as follows: the difference of the discharge capacity D is 0-5%, the difference of constant voltage charging time CV-T is less than or equal to 3min, the difference of open circuit voltage OCV1 and OCV2 is less than or equal to 5mV, the difference of the difference between self-discharge OCV1 and OCV2 (voltage drop, OCV2-OCV1) is less than or equal to 5mV, the difference of high-frequency alternating current internal resistance Rh is 0-25%, and the difference of low-frequency alternating current internal resistance Rl is 0-25%.

Meanwhile, the invention also provides a high-rate lithium titanate battery pack which is composed of lithium titanate single batteries (connected in series and/or in parallel) screened by the method and good in consistency.

The main idea of the invention is that for self-discharge screening, as can be seen from the open-circuit voltage curves of different states of charge of the lithium titanate battery in fig. 1, the voltage of the battery is linearly changed along with the change of the SOC within the range of 5% -30% SOC, at this stage, the battery is in an unstable interval, the self-discharge rate is relatively high, the voltage is more gentle after the SOC is greater than 30% SOC, the self-discharge differential screening is not facilitated within a short time, when the SOC is continuously increased to a high state of charge, the positive electrode potential is higher, and the battery is adversely affected when being placed at high temperature, so the self-discharge screening range is set to be 5% -30% SOC, preferably 10% -20% SOC, and the screening of the battery with larger self-discharge within a short time can be achieved through a high-temperature placing. On the other hand, for the screening of the internal resistance of the battery, the test results of different frequency bands of the battery can reflect different internal resistances under the alternating current test condition, wherein the high-frequency alternating current internal resistance mainly reflects the ohmic internal resistance of the battery, and the low-frequency alternating current internal resistance can reflect the internal polarization internal resistance of the battery.

Compared with the conventional dynamic direct current internal resistance test such as an HPPC method, the static alternating current internal resistance test adopted by the invention has the following advantages: (1) the response time of the static internal resistance test is only about 0.1s, so that the internal polarization internal resistance and the ohmic resistance of the battery can be tested or reflected more quickly, and the screening time is greatly shortened; (2) the method has the advantages that large-current charging and discharging tests are not needed, the operation method is simpler and more convenient, and the current limit of charging and discharging equipment is not needed to be considered, so that the screening method is wider in range of applicable battery types; (3) the battery is always in a near-steady state in the testing process, and belongs to nondestructive testing; (4) the equipment and electric power cost in the screening process are greatly saved.

In addition, the method of the invention also adds parameter screening of constant voltage charging time, and the parameter mainly reflects the internal polarization internal resistance of the battery. In the constant-current constant-voltage charging method, the constant-voltage step is trickle charging, and the longer the charging time is, the smaller the charging amount in the earlier constant-current charging stage is proved, namely the larger the internal polarization internal resistance of the battery is, and the screening accuracy degree is further supplemented. The parameter is mainly used as an input of the whole battery screening scheme so as to provide a more accurate and comprehensive screening result.

Compared with the conventional battery screening consistency method, the method not only considers all conventional screening parameters, but also provides an efficient self-discharge screening process and a simplified battery internal resistance testing method, improves the battery screening efficiency to the maximum extent on the basis of accurately judging the battery consistency, and ensures that the battery screened by the method has better consistency under the large-multiplying-power (more than 10C) charging and discharging working condition.

Drawings

FIG. 1 is a graph of open circuit voltage for lithium titanate batteries at different states of charge.

FIG. 2 is a comparison graph of the trends of dynamic internal resistances of cells tested by the low-frequency AC impedance method and the HPPC method in example 1 of the invention.

Fig. 3 is a graph comparing large-rate sustained discharge curves of 24V batteries 400A of 11 lithium titanate unit cells 11S1P sorted by the methods of example 1, example 2 and comparative example 1.

Fig. 4 shows a discharge curve of a 24V battery pack 400A of 11 lithium titanate unit cells sorted in example 1, 11 lithium titanate unit cells constitute 11S1P, and 11 unit cells are continuously discharged at a high rate.

Fig. 5 shows a discharge curve of 11 lithium titanate unit cells sorted out in comparative example 1, which is a 24V battery pack 400A of 11S1P and continuously discharged at a high rate for 11 unit cells.

Detailed Description

In order to more clearly illustrate the technical solutions and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings, examples and comparative examples.

Example 1:

the battery with the rated capacity of 25Ah, the anode of the ternary material and the cathode of the lithium titanate material is taken as an example. In this example, 11 batteries were screened to form a 24V 11 series battery pack.

The first step is as follows: charging the pre-charged battery on a test cabinet to 2.8V at a constant current and a constant voltage of 1C, stopping the constant voltage charging current to 0.05C A, charging and discharging for 3 times, and recording the discharge capacity D and the constant voltage charging time CV-T; the battery is charged to 10% SOC (CC-CV is charged to 2.365V, constant voltage cutoff current is 0.05CA), and open-circuit voltage OCV1 is measured after the battery is placed for 1h at room temperature;

the second step is that: the battery is put into a thermostat at 55 ℃ for 10 hours, the battery is taken out and cooled to room temperature, and then the open circuit voltage OCV2 of the battery, the static internal resistance Rh at the frequency of 1kHz and the single-point internal resistance Rl at the frequency of 2Hz are measured.

The discharge capacities D, CV-T, OCV1, OCV2-OCV1, OCV2, Rh and Rl measured above were compared, and the conditions were screened: the difference of the discharge capacity is 0-5%, the constant-voltage charging time is less than or equal to 2min, the difference of the open-circuit voltage OCV1 is less than or equal to 5mV, the difference of the open-circuit voltage OCV2 is less than or equal to 5mV, the difference between the self-discharge voltage drop OCV1 and the OCV2 is less than or equal to 5mV, the difference of the high-frequency internal resistance Rh is 0-25%, and the difference of the low-frequency. In this example, 11 qualified single batteries were screened, and the measurement parameters thereof are detailed in table 2.

Example 2:

this example also randomly tested 20 batteries, using a 25Ah ternary/lithium titanate battery as an example.

Test procedure the same procedure as in example 1 was followed except that the charging SOC of the first step in example 1 was adjusted to 20% SOC and the battery was left in a 55 ℃ incubator for 12 hours.

Table 3 shows the detailed screening parameters for all 20 batteries of example 2. Although the battery capacities, the constant voltage charging time, the high-frequency alternating current internal resistances, the OCVs 1 and the OCVs 2 of the 8#, the 13# and the 17# are small in difference with other batteries, the low-frequency alternating current internal resistances exceed the screening range of 0-25%, and therefore the three batteries are judged to be unqualified batteries. Among the other qualified batteries, 11 batteries (1-3 #, 9-12 #, 14#, 18-20 #, respectively) are further randomly selected to form a battery pack of 11 strings, and the discharge performance of the battery pack under the heavy current of 400A is comparatively tested, and the result is shown in figure 3.

For better comparison and demonstration of the accuracy of the invention, the dynamic internal resistance of the batteries is tested by the HPPC method in both the example 1 and the example 2, and the dynamic internal resistance and the low-frequency alternating current internal resistance of the 11 batteries screened in the example 1 have the change trends shown in the attached figure 2 and the table 2. Example 2 dynamic internal resistance data for randomly selected cells tested using the HPPC method are shown in table 3. From the test results of the two sets of examples it can be derived: the low-frequency alternating-current internal resistance of the invention has the same trend as that of the HPPC method, and the impedance tested by adopting the single-point low-frequency battery impedance analyzer can accurately reflect the dynamic internal resistance of the battery, thereby avoiding using a dynamic internal resistance testing method with high energy consumption and certain damage force, and simultaneously ensuring the accuracy of the consistency screening of the dynamic internal resistance.

Comparative example 1:

comparative example a conventional battery screening procedure was used.

The first step is as follows: charging the pre-charged battery on a test cabinet to 2.8V at a constant current and a constant voltage of 1C, stopping the constant voltage charging current to 0.05C A, charging and discharging for 3 times, and recording the discharge capacity and the constant voltage charging time CV-T; the battery is charged to 85% soc (CC-CV is charged to 2.5V, constant voltage cutoff current is 0.05CA), and open-circuit voltage OCV1 is measured after the battery is placed for 1h at room temperature;

the second step is that: after the battery was left to stand at normal temperature for 15 days, the battery open-circuit voltage OCV2 and the high-frequency alternating-current internal resistance Rh at a frequency of 1kHz were measured.

The discharge capacities D, CV-T, OCV2-OCV1, OCV2, Rh measured above were compared, and the screening conditions were: the difference of the discharge capacity is 0-5%, the constant voltage charging time is less than or equal to 2min, the difference of the open-circuit voltage OCV2 is less than or equal to 5mV, the difference of the self-discharge OCV1 and OCV2 is less than or equal to 5mV, and the difference of the static internal resistance Rh is 0-25%. In this example, 11 qualified single batteries were screened, and the measurement parameters thereof are detailed in table 1.

Table 1 comparative example 1 test data

Table 2 example 1 test data

Table 3 test data of each unit cell in example 2

11 qualified batteries screened from each of example 1, example 2 and comparative example 1 were assembled into 11 strings of modules and subjected to a discharge test at a large current of 400A, and the results are shown in fig. 3 to 5. The test results show that the consistency of the single batteries of the lithium titanate 11 string modules screened in the examples 1 and 2 is far better than that of the single batteries of the comparative example 1 under the large current of 400A. The screening of the cells was completed in 15 to 17 hours as compared with the comparative example.

In conclusion, the method takes the parameters of the battery discharge capacity, the open-circuit voltage, the constant voltage time, the self-discharge, the static ohmic internal resistance, the polarization impedance and the like into consideration, can comprehensively and quickly screen the battery, and the sorted battery can meet the use condition that the requirement on the consistency is severer under the condition of high multiplying power. The sorting method provided by the invention is simple to operate and is very beneficial to industrial popularization and application.

Claims

1. A consistency screening method for a lithium titanate single battery with high multiplying power is characterized by comprising the following steps:

step 1: charging and discharging the battery to be sorted, and recording the battery discharge capacity D and the constant voltage charging time CV-T; the battery was then charged to a specific state of charge (SOC), at which time the open circuit voltage OCV1 was measured;

step 2: standing the battery obtained in the step 1 in a high-temperature T1 environment for a certain time T1, taking out the battery, cooling the battery to room temperature, and measuring open-circuit voltage OCV2, high-frequency alternating-current internal resistance Rh and low-frequency alternating-current internal resistance Rl;

and step 3: and comparing the discharge capacity D, the constant-voltage charging time CV-T, the open-circuit voltage OCV1, the voltage drop (OCV2-OCV1), the open-circuit voltage OCV2, the high-frequency alternating-current internal resistance Rh and the low-frequency alternating-current internal resistance Rl of each battery to be sorted, and screening lithium titanate single batteries which have better consistency and meet the discharge of the large-current working condition according to the parameter screening conditions.

2. The screening method for the consistency of high-rate lithium titanate single cells according to claim 1, wherein in the step 1, the number of charging and discharging is not less than 3.

3. The screening method for consistency of high-rate lithium titanate unit cells according to claim 1 or 2, wherein in the step 1, the specific state of charge SOC ranges from 5% to 30%, preferably from 10% to 20%.

4. The screening method for screening lithium titanate battery cells for high rate according to any one of claims 1 to 3, wherein in the step 1, the battery is charged to a specific state of charge SOC by a constant current-constant voltage charging method.

5. The screening method for the consistency of high-rate lithium titanate unit batteries according to claim 1, wherein in the step 2, the high temperature T1 is 45-65 ℃, and the high temperature rest time T1 is 5-15 h.

6. The screening method for the consistency of high-rate lithium titanate single cells according to claim 1 or 5, wherein in the step 2, the high temperature T1 is 45-55 ℃, and the high temperature time T1 is 8-12 h.

7. The screening method for the consistency of the lithium titanate single battery with high magnification according to claim 1, characterized in that in the step 2, the measurement frequency of the high-frequency alternating internal resistance Rh is 1kHz, and the measurement frequency of the low-frequency alternating internal resistance Rl is 1 Hz-2 Hz.

8. The method for screening consistency of high-rate lithium titanate single cells according to any one of claims 1 to 7, wherein in the step 3, the screening conditions of parameters of each battery to be sorted are as follows: the difference of the discharge capacity D is 0-5%, the difference of constant voltage charging time CV-T is less than or equal to 3min, the difference of open circuit voltage OCV1 and open circuit voltage OCV2 is less than or equal to 5mV, the difference of voltage drop (OCV2-OCV1) is less than or equal to 5mV, the difference of high frequency alternating current internal resistance Rh is 0-25%, and the difference of low frequency alternating current internal resistance Rl is 0-25%.

9. The method for screening consistency of high-rate lithium titanate single batteries according to any one of claims 1 to 8, wherein the screened batteries can meet the application of operating mode rate of more than 10 ℃.

10. A lithium titanate battery pack for high rate use, characterized in that the battery pack consists of lithium titanate single batteries which are screened according to the screening method of any one of claims 1 to 9 and have good consistency.