Failure mode and effects analysis of LFP battery module

The analysis of the charge/discharge curve helps judge the quality of cells and figure out some strange behaviors of the battery module. Especially, many unusual behaviors won’t exhibit on the appearance. It’s important to establish the charge/discharge profile database for effective manufacturing and troubleshooting. In this talk, the basic charge/discharge method of Li-ion battery, simple equivalent circuit model of battery, general charge/discharge curve of LFP battery will be introduced. Then a case-by-case failure mode and effects analysis will be presented. Up to ten cases are discussed in the slides.Dr. Hsien-Ching Chung was invited by Dr. Jim Lee (the chairman of Taiwan Battery Association) to give a talk about "Failure mode and effects analysis of LFP battery module" in the conference, "2018 Taiwan-Japan exchange conference on battery materials and battery manufacturing technologies." The conference was held in Center for Space and Remote Sensing Research, National Central University, Taoyuan, Taiwan on Dec. 18, 2018. There were about 20 keynote speakers and 150 participants. It's a good opportunity to realize new technologies in the battery industry and the future of the energy industry.


 Introduction
To raise the standard of Taiwan batteries industry and enhance the international competitiveness of the market, the Industrial Technology Research Institute (ITRI) established "Taiwan Battery Industry and Technology Development Union" in 1996, with more than 40 domestic battery industries which contain the up, middle and down-stream manufacturers. With the economy changes and the development of electronics industry, the multi-boom growth of the battery industry, The Taiwan Battery Association was formally founded in April 2006 . The Taiwan Battery Association (TBA) was established as a non-profit organization. It was devoted to meet the cooperation and development of Taiwan's battery industry, to enhance the international competitiveness of the battery industry, to assist in establishing the development strategy and direction of Taiwan's battery industry and to establish the battery industry's strategy and R&D alliances.

Abstract
The analysis of the charge/discharge curve helps judge the quality of cells and figure out some strange behaviors of the battery module. Especially, many unusual behaviors won't exhibit on the appearance. It's important to establish the charge/discharge profile database for effective manufacturing and troubleshooting. In this talk, the basic charge/discharge method of Li-ion battery, simple equivalent circuit model of battery, general charge/discharge curve of LFP battery will be introduced. Then a case-by-case failure mode and effects analysis will be presented. Up to ten cases are discussed in the slides. Basic charge/discharge method

CC-CV mode charge method
The battery is charged at a constant current until the voltage reaches a setting value, and then the voltage is held constant as the current decays to a cutoff current.

CC mode discharge method
The battery is discharged at a constant current until the voltage reaches a setting value. 7 Equivalent circuit model of battery Rest: After discharge (charge) process, the voltage will gradually increase (decrease).

DCIR:
A voltage drop at the beginning of discharge.
A voltage raise at the beginning of charge. 9 The air conditioner is turned off after work.
Failure mode and effects analysis: A case-bycase study 1. Cell 2. Pack/Module The following cases are picked from RD database.
Case 1: Bad cell (abnormal Charge/discharge curve) The discharge curve isn't smooth. Case 5: Why the battery become unbalance at CV mode?
The 8s battery is made by new cells with high consistency.
When the battery is charged at CV mode with a high voltage near the battery limitation, the voltage unbalance appear, although the unbalance cannot be observed from the total voltage.
Case 6: Why the cutoff voltage isn't at 2 V per cell?
BMS setting: the relay will be turned off once one of the cells is under 2 V.
Some people have a question. Why the power is cut before the voltage reaches 16 V? (This is an 8s system.) 16

CTE
Case 7: Something wrong in manufacturing process will be figured out.
The 8s battery is made by new cells with high consistency.
Why the 5 th cell exhibit a larger DCIR than others?
17 Case 8: A poor battery charging without BMS.
The voltages of bad cells rise too fast.
The total voltage won't tell you the overcharging. 18