Safety Hazards(1)Thermal Runaway RiskA short - circuit can cause an enormous current to pass through the battery instantly. According to Joule's law (², whereis heat,is current,is resistance, andis time), in the case of a short - circuit, du...
A short - circuit can cause an enormous current to pass through the battery instantly. According to Joule's law (, where is heat, is current, is resistance, and is time), in the case of a short - circuit, due to the small resistance and extremely large current, a large amount of heat will be generated in a very short time. For lithium - iron - phosphate batteries, this heat may trigger a series of exothermic reactions inside the battery.
When the temperature rises to a certain level, materials such as the separator inside the battery may melt and rupture. The main function of the separator is to prevent the positive and negative electrodes from direct contact. Once the separator fails, the positive and negative electrodes of the battery will come into direct contact, further exacerbating the short - circuit situation and forming a vicious cycle, which ultimately leads to thermal runaway. In a state of thermal runaway, the battery may catch fire or explode, posing a serious threat to the surrounding environment and personal safety.
(2) Electrolyte Leakage
The huge short - circuit current can cause a sharp increase in the internal pressure of the battery. The casing of lithium - iron - phosphate batteries is usually made of aluminum - plastic film or metal. When the internal pressure exceeds the limit that the casing can withstand, the casing may rupture.
The electrolyte inside the battery will then leak. The electrolyte is generally a mixture of organic solvents and lithium salts and is corrosive. If the leaked electrolyte comes into contact with human skin or eyes, it can cause chemical burns; if it comes into contact with other equipment or metal parts, it may cause corrosion and further damage the equipment.
(3) Gas Release
During a short - circuit, the chemical reactions inside the battery will intensify. Besides generating heat, a large amount of gas will also be produced. These gases mainly include flammable or toxic gases such as hydrogen and carbon monoxide.
When the gas accumulates to a certain concentration in a relatively closed space, it will form an explosive - hazard environment. Once it encounters an ignition source, such as a spark generated by a short - circuit, an explosion may occur, and the released toxic gases will also harm human health.
Battery Performance Hazards
(1) Battery Capacity Fade
The large current generated during a short - circuit can cause irreversible damage to the positive and negative electrode materials of the battery. In terms of the positive electrode material, the crystal structure of lithium - iron - phosphate () may be damaged due to the impact of the large current, resulting in the loss of active materials.
For the negative electrode material, such as graphite, the large current may cause the solid - electrolyte - interface (SEI) film on the negative electrode surface to rupture and reform. The repeated destruction and repair of the SEI film will consume lithium ions in the battery, reducing the reversible capacity of the battery and leading to a rapid fade in battery capacity.
(2) Internal Resistance Increase
The large current during a short - circuit can cause the internal temperature of the battery to rise sharply. This high - temperature environment may lead to physical and chemical changes in the conductive materials inside the battery (such as electrodes and current collectors). For example, the electrode materials may agglomerate or sinter, reducing the conductivity of the battery.
At the same time, the electrolyte inside the battery may decompose or dry out under the action of high temperature and large current, which will also increase the internal resistance of the battery. The increase in internal resistance will further reduce the charge - discharge performance of the battery, causing the battery to heat up severely during subsequent use and reducing the energy - conversion efficiency.
(3) Worsening of Battery Consistency
When multiple lithium - iron - phosphate batteries are connected in parallel, the impact of a short - circuit on each battery may vary. Even a slight difference, such as in battery internal resistance and capacity, will be amplified during subsequent charge - discharge processes.
Batteries that are more severely affected by the short - circuit may fail prematurely, making the performance of each battery in the parallel battery pack inconsistent. This inconsistency will affect the performance of the entire battery pack, such as reducing the total capacity of the battery pack and shortening the cycle life of the battery pack.
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