Mechanism of Thermal Runaway in VRLA Batteries and Methods to Suppress it
Abstract
The technical objective of the current project is to disclose the mechanism of the processes leading to Thermal Runaway (TRA) in VRLA batteries during overcharge. The TRA effect is related to an uncontrolled temperature rise reaching very high values of 80-100 degrees C on battery overcharge. An appropriate experimental set up was built for the purposes of the project work. It allowed us to monitor 5 cell parameters: current, positive and negative plate potentials, temperature and gassing rate of the cells. The experiments show that TRA may occur when the cell is exposed on continuous overcharge at a voltage higher than a certain critical value. It has been established that the reactions that proceed at the two types of electrodes are in selfaccelerating interrelation. At the positive plates, a reaction of water decomposition and evolution of oxygen proceeds. O2 is reduced at the negative plates whereby heat is released. Consequently, the temperature in the cell rises. The elevated temperature accelerates the reaction of water decomposition and oxygen evolution at the positive plates. Thus, the processes at the two types of plates accelerate each other. However, with increase of temperature, the heat exchange between the cell and the surrounding medium increases. When the exchanged heat becomes equal to the heat generated in the cell by the reactions at the negative plates, the cell temperature reaches a maximum. This phenomenon was called "self-accelerating interrelation between the reactions of the oxygen cycle (SAIR)", it refers to the spontaneous current increase. The thermal runaway (TRA), reflecting the temperature rise, and the SAIR are two sides of one and the same phenomenon designated by SAIR-TRA. Up to now the processes involved in the above phenomenon have been known as TRA effect. The increase in cell temperature and current during TRA depends strongly on the type of regulator used, the cell voltage, and the history of battery operation.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 2004
- Accession Number
- ADA524681
Entities
People
- Detchko Pavlov
Organizations
- Bulgarian Academy of Sciences