Lithium batteries, known for their high energy density, are prone to thermal runaway, which can be triggered by three types of abuse: mechanical, electrical, and heat. Mechanical abuse involves external forces such as collisions, extrusions, and punctures, compromising the battery’s structure. Electrical abuse includes both internal and external short circuits, overcharging, and discharging, which can lead to internal damage. Thermal abuse results from external heating of the battery, worsening the situation.
The process of thermal runaway begins with mechanical abuse, leading to internal diaphragm breakage and resulting in an electrical short circuit. Subsequently, electrical abuse triggers thermal abuse, as short circuits generate heat, initiating chemical reactions at high temperatures. This further exacerbates thermal abuse, creating a self-sustaining cycle. When the accumulated heat reaches a critical level, thermal runaway occurs, potentially leading to an explosive event.
This article provides a detailed analysis of the chemical reactions inside lithium batteries, focusing on positive, negative, and electrolyte perspectives. These reactions are carefully classified based on various trigger temperatures. The study introduces an innovative approach, suggesting the use of gases produced during lithium battery heating for early warning diagnosis. By distinguishing abnormal gases from normal ones, these gases serve as crucial indicators for potential thermal runaway.
Research on Internal Chemical Reactions of Lithium Batteries
Theoretical Basis
It is essential to comprehend the structure of lithium batteries. These batteries consist of a positive electrode, a negative electrode, and an electrolyte, operating based on positive electrode discharge and charging reactions. The electrolyte contains two or more solvents and one or more lithium salts, ensuring the battery’s peak performance.
Research on Chemical Reactions
Positive Electrode and Electrolyte Reaction:
The thermal breakdown of the positive electrode releases oxygen, a key factor in triggering thermal runaway. This oxygen, along with other reactions, sets off a chain effect that leads to thermal runaway.
Negative Electrode and Electrolyte Reaction:
The negative electrode’s surface area is crucial in its reaction. When the Solid Electrolyte Interface (SEI) decomposes, it exposes the negative electrode to the electrolyte, impacting subsequent reactions.
Electrolyte Reaction:
The breakdown of solute LiPF6 and its interactions with other components such as DEC and HF influence the overall chemical environment within the battery.
Trigger Sequence of Chemical Reactions
The chemical reactions inside lithium batteries follow a sequence of trigger temperatures. Each reaction stage, from LiPF6 decomposition at 60-70°C to diaphragm dissolution at 130-190°C, is crucial for understanding the thermal runaway process.
Early Warning and Diagnostic Strategy
Early warning diagnosis relies on distinguishing gases produced under normal and abnormal conditions. The unique content, change rate, and type of these gases offer valuable clues for early warning systems. Abnormal gases such as CO2 and PF5 differ significantly from normal gases like CO and C2H4, allowing for targeted sensor implementation and accurate diagnosis thresholds.
