Consistency screening method for high-rate lithium titanate unit cells

Abstract

The invention relates to a consistency screening method for high-rate lithium titanate unit cells. The screened lithium titanate cells have high consistency under a high-current discharge working condition. The method comprises the following steps of adjusting the cells to a specific charge state and storing the cells at elevated temperature for a short time so as to quickly screen out the cells with large self-discharge; and then carrying out a specific single-point high-frequency and low-frequency alternating-current impedance test on the cells stored at the elevated temperature so as to directly reflect the ohmic internal resistance and the polarization internal resistance of the cells. According to the method, self-discharge and dynamic internal resistance of the cells are rapidly andaccurately evaluated while the parameters of conventional discharge capacity, open-circuit voltage, constant voltage time, static internal resistance and the like are taken into consideration, and thescreening result is more comprehensive, accurate and effective; and according to the scheme, the consistency screening of the cells can be completed within one day, the screening cycle of the cells can be greatly shortened, the operation is simple and convenient, the energy consumption is low, and the method is suitable for large-scale batch application of an automatic production line.

Description

technical field [0001] The invention belongs to the technical field of battery detection, and relates to a consistency screening method for a lithium titanate single battery with a large rate. Background technique [0002] Lithium titanate battery's unique high safety, excellent high-current charge and discharge performance, long life and low temperature characteristics have become the preferred choice for fast-charge lithium-ion power batteries, rail transit vehicle lithium batteries and start-stop system power supplies. In practical applications, lithium titanate batteries need to be used in the form of series-parallel battery packs, and the charging and discharging conditions can reach about 10C. This series-parallel mode has extremely strict requirements on the consistency between single batteries. Therefore, the lithium titanate battery with high consistency screened out quickly, efficiently and accurately will help to improve the service life, safety and energy efficie...

AI Technical Summary

Problems solved by technology

[0003] Battery consistency screening needs to comprehensively consider multiple parameters such as the discharge capacity, platform voltage, open circuit voltage, battery internal resistance, and self-discharge of the single battery. However, there are few parameter settings in the existing screening methods, and the screening results are accurate and precise. low

In addition, for the testing of specific parameters such as self-discharge and polarization internal resistance, the existing methods (for example, the commonly used HPPC method for measuring polarization internal resistance) take a long time, consume a lot of energy, are more complicated to operate, and require a large current Pulse charging and discharging equipment, so it is not suitable for industrial application

For example, the Chinese patent application with application number 201710818877.5 discharges the battery to 1.3-1.8V (about 46-64% SOC ) within the range of high temperature, and the battery with excessive self-discharge is screened out by testing the open circuit voltage difference before and after the storage, but the screening time used by the application is still relatively long in the selected voltage range, about 1-2 days, and the application The method does not take into account the difference in the polarization internal resistance of the battery

The Chinese patent application with application number 201710773164.1 takes into account both static parameters and dynamic parameters such as DC internal resistance and self-discharge. However, this method must perform a high-rate pulse discharge of 10 to 20C on the battery. Taking Example 1 as an example, a 250A Pulse charging and discharging with high current, which not only requires high-rate pulse charging and discharging equipment, but also requires high equipment investment and high energy consumption. It may also cause damage to the factory battery itself. 10 days, a long time, and cumbersome calculation process, the screening efficiency is low

The Chinese patent application with application number 201710846568.9 screens batteries through multiple vibrations, high temperature shelving and multiple DC internal resistance tests. The discharge current is large (the maximum current when the car is running), and the screening process is complicated and takes a long time.

Application No. 201710824747.2 Chinese patent application tests the AC impedance of multiple batteries at multiple different preset AC frequencies to dynamically screen the batteries. Although this method can achieve fast grouping, it is difficult to reduce the self-discharge batteries screened out

Images