Causes and Prevention Strategies for Lithium Battery Failure

Written by :

Mari

1.What is lithium battery failure?

Lithium battery failure refers to the condition where lithium-ion batteries are unable to maintain their design performance or achieve expected lifespan due to various reasons. Such failure may manifest as decreased capacity, increased internal resistance, slower charging speed, shortened cycle life, poor consistency, self-discharge, and safety risks such as thermal runaway, swelling, electrolyte leakage, lithium plating, short circuits, and expansion deformation.

2.Reasons for lithium battery failure

(1) Charging cycle count

The lifespan of lithium-ion batteries is related to the number of charging cycles. After a certain number of cycles, the battery capacity will decrease, leading to failure.

(2) Overcharging and over-discharging

Extended periods of overcharging or over-discharging can cause chemical changes inside the battery, reducing its performance.

(3) High-temperature environment

High temperatures accelerate chemical reactions within the battery, leading to aging and performance degradation.

(4) Physical damage

Physical damage to the battery, such as impacts or compression, may cause internal short circuits or damage, resulting in failure.

3.Mechanisms of lithium battery failure

(1) Lithium ion migration

During charge and discharge cycles, lithium ions migrate between positive and negative electrodes, causing structural changes in electrode materials and reducing battery performance.

(2) Electrolyte degradation

Electrolyte degradation leads to unstable chemical reactions within the battery, affecting its cycle life.

(3) Formation of solid electrolyte interface (SEI film)

During charge and discharge cycles, a solid electrolyte interface forms in lithium-ion batteries. As the number of cycles increases, the continuous formation of this interface increases resistance, reducing battery performance.

4.Failure modes of lithium batteries

The failure modes of battery systems mainly include capacity decay, increased internal resistance, and polarization. Depending on the structure and composition of the battery system, three different levels of failure modes can be distinguished: cell failure mode, battery management system (BMS) failure mode, and pack system integration failure mode.

A. Cell failure mode

The failure modes of cells can be divided into safety failure modes and non-safety failure modes. Safety failure modes of cells mainly include:

(1) Internal short circuit of cells

Defects during cell production or long-term vibration and external forces can cause cell deformation, eventually leading to internal short circuits. Once a serious internal short circuit occurs, it cannot be controlled, external protection measures are ineffective, and smoke or combustion will inevitably occur.

(2) Leakage of cell unit

External damage, collisions, improper installation leading to seal structure damage, welding defects, insufficient sealing glue, etc., may cause cell leakage. After the cell leaks, the insulation of the entire battery pack fails, and when there are multiple insulation failure points, an external short circuit occurs.

(3) Lithium plating on the negative electrode of the battery

Improper use of the battery, overcharging, low-temperature charging, and high-current charging can all cause lithium plating on the negative electrode of the battery. After lithium plating occurs on the negative electrode, lithium metal cannot be reduced, leading to irreversible capacity decay. When lithium plating reaches a certain severity, lithium dendrites form, puncturing the diaphragm and causing an internal short circuit. Therefore, charging at low temperatures should be strictly prohibited when using lithium-ion batteries.

(4) Expansion and swelling of cell

There are many reasons for the occurrence of swelling, such as gas generated by side reactions inside the battery, which can cause the battery to swell. The swelling problem can be controlled by strictly controlling the moisture content during the cell production process. Once the battery swells, leakage and other issues may occur.

The safety failure risk of cells is relatively high. In contrast, non-safety failure only causes performance issues such as poor temperature consistency, excessive self-discharge, reduced low-temperature discharge capacity, and capacity decay.

B. BMS failure mode

(1) Failure of BMS voltage detection leading to overcharging or over-discharging of the battery

Poor connection or poor contact during connection or pressure leads to the failure of the voltage detection line, and the BMS has no voltage information, so charging does not stop when it should. Battery overcharging may cause fire and explosion. Most lithium iron phosphate batteries only smoke when overcharged above 5V, but once lithium cobaltate batteries are overcharged, explosions may occur.

Moreover, overcharging can easily cause the decomposition of the electrolyte in lithium-ion batteries, resulting in battery swelling. In severe cases, smoke and fire may occur. Over-discharge of the battery can cause damage to the molecular structure of the positive electrode material of the battery, thereby preventing the battery from being recharged. At the same time, excessively low battery voltage causes the decomposition of the electrolyte and drying, resulting in lithium plating and internal short circuits of the battery. When designing the system, reliable voltage acquisition lines should be selected, and strict control should be carried out during production to prevent the failure of the voltage acquisition line.

(2) Failure of BMS current detection

The failure of the Hall sensor results in the BMS not being able to collect current, and the SOC cannot be calculated, resulting in large deviations. The failure of current detection may cause excessive charging current. Large charging current will cause large internal heating of the battery, and the temperature will exceed a certain temperature, which will cause the diaphragm to solidify and reduce the capacity, severely affecting the battery life.

(3) Failure of BMS temperature detection

The failure of temperature detection leads to excessively high working temperature of the battery, irreversible reactions occur in the battery, which has a great impact on the battery capacity and internal resistance. The calendar life of the cell is directly related to the temperature. The number of cycles at 45°C is half of that at 25°C. In addition, high temperature can easily cause battery swelling, leakage, explosion, etc. Therefore, the temperature of the battery should be strictly controlled between 20-45°C during use, which can not only effectively improve the battery’s service life and reliability, but also effectively avoid the short circuit caused by lithium plating during low-temperature charging of the battery and high-temperature thermal runaway.

(4) Insulation monitoring failure

Insulation failure occurs when the power battery system deforms or leaks. If it is not detected by the BMS, it may cause electric shock to personnel. Therefore, the requirements for the sensors monitored by the BMS system should be the highest, and avoiding the failure of the monitoring system can greatly improve the safety of the power battery.

(5) Failure of electromagnetic compatibility communication

For the BMS system, electromagnetic compatibility mainly tests its ability to resist electromagnetic interference. Electromagnetic interference will cause the failure of BMS communication, leading to the above-mentioned problems.

(6) Large deviation in SOC estimation

At present, there is generally a deviation in the SOC. The general inspection standard requires a deviation of less than 5%. Most manufacturers’ BMSs should be difficult to achieve because of the complexity of the usage environment, and the actual use SOC error will become larger and larger.

C. Pack system integration failure mode

(1) Failure of busbar

If it is bolted, in the later use process, the oxidation and falling off of the bolt or vibration will cause the bolt to loosen, which will cause a large amount of heat at the conductor connection, and in extreme cases, it will cause the power battery to catch fire.

(2) Failure of the main circuit connector of the power battery system

The high-voltage line of the power battery system is connected to the external high-voltage system through a connector. The connector performance is unreliable, and virtual connection occurs under vibration, resulting in high-temperature ablation of the connector. Generally, the connector temperature exceeds 90 degrees, and connection failure will occur. Therefore, in the system design, the connector needs to be equipped with a high-voltage interlocking function, or a temperature sensor should be added to the connector to monitor the temperature of the connector at all times to prevent connector failure.

(3) Adhesion of high-voltage contactors

The contactor has a certain number of load-breaking, most of which will ablate when the contactor closes under large current. In system design, a dual-relay scheme is generally used to close control in sequence to avoid the sticking of high-voltage contactors.

(4) Failure of overcurrent protection of fuse

The selection and matching of fuses in high-voltage system components need to be comprehensively considered. Vibration or external collision and squeezing cause deformation of the power battery, sealing failure, and reduction of IP level. Therefore, in system design, attention should be paid to the collision protection of the battery box structure.

5.Prevention and treatment methods of lithium battery failure

(1) Proper Charging and Discharging

Avoid overcharging and overdischarging, adopt appropriate charging and discharging strategies to delay battery aging.

(2) Temperature Control

Avoid exposing the battery to high-temperature environments to slow down the rate of battery aging.

(3) Use of Battery Management System (BMS)

The BMS can monitor the battery’s status, detect problems in advance, and take measures to protect the battery from overcharging, overdischarging, and other effects.

(4) Use of Battery Management System