Thermal runaway in a power lithium-ion battery pack indicates a safety issue and requires immediate attention; otherwise, it could pose a danger and cause harm to the user.
Since thermal runaway in power lithium-ion battery packs is a very dangerous event, it is important to understand the causes of thermal runaway and how to solve it. Ideally, we should learn from the causes and take precautions when using lithium-ion battery packs to prevent thermal runaway.
Causes of thermal runaway in power lithium-ion battery packs
mechanical abuse
When subjected to external forces, lithium-ion battery packs are affected and deformed, and different parts of the pack undergo relative displacement. When lithium-ion battery cells are subjected to external forces, internal collisions, compression, and punctures also constitute mechanical abuse.
Among mechanical abuse, puncture is the most dangerous. When a conductor is inserted into the battery body, it causes a direct short circuit between the positive and negative electrodes. Compared with collisions and squeezing, which only result in a probability of internal short circuits, the heat generated during puncture is more intense, and the probability of thermal runaway is higher.
electrical abuse
Electrical abuse of lithium-ion battery packs generally includes several forms such as external short circuit, overcharging, and over-discharging. Among these, overcharging is the most likely to develop into thermal runaway.
An external short circuit occurs when two conductors with a voltage difference are connected outside the battery cell. A crucial step between an external short circuit and thermal runaway is excessively high temperature. The battery temperature rises only when the heat from the external short circuit cannot dissipate effectively, triggering thermal runaway.
Overcharging, due to its high energy content, is one of the most dangerous forms of electrical misuse. The presence of heat and gas are two common characteristics of the overcharging process. The heat generated comes from ohmic heat and side reactions.
The abuse mechanism of over-discharge differs from other forms of abuse, and its potential danger is far greater than commonly believed. Over-discharge induces the dissolution and migration of copper ions through the membrane, forming copper dendrites with a lower potential on the cathode side. As growth increases, these copper dendrites may penetrate the membrane, leading to severe thermal runaway problems.
Heat abuse
Localized overheating is a typical thermal abuse situation that can occur in battery packs. Thermal abuse rarely occurs in isolation; it often develops from mechanical and electrical abuse and is ultimately the link that directly triggers thermal runaway.
Regarding thermal runaway caused by mechanical abuse, the best course of action is to replace the faulty lithium-ion battery pack and discard the battery, which has suffered physical damage.
