Cell failure can occur due to various reasons. Proper design and high manufacturing quality are the keys to having safe and high-performance batteries on the market. Battery design needs to take into account all the intended usage conditions and also the foreseeable misuse cases in order to maintain battery safety. Manufacturing flaws of lithium-ion cells have led to several safety issues in the past. Manufacturing quality relies on the high-level quality of raw materials, impurity control, manufacturing devices, process control, and inspection.
Both time and usage affect the ability of a lithium-ion cell to store energy and deliver power, seen as capacity fade and impedance increase. This aging of cells occurs both during storage and during repeated charge and discharge cycles in the normal operation of the powered device.
Lithium-ion cells are designed to work at specific conditions. The harder the usage conditions, the faster is the aging and thus the performance degradation. Lithium-ion cells are designed and specified to tolerate certain voltages, currents, and operating temperatures. In addition to capacity and power fade, exceeding these allowed operating limits can lead to the damaging of the active and inactive components. Furthermore, lithium-ion cells are not inherently tolerant to abusive conditions such as over-charging, over-discharging, short-circuit (external or internal), extreme temperatures, or mechanical damage. Exposure to abusive conditions may lead to severe cell failure.
In the worst-case scenario, improper operation or abusive conditions may lead to a thermal runaway of the battery. This failure can for example occur from a cell temperature increase caused by an internal short-circuit, which may result from impurity particles, poor cell design or manufacturing quality, or lithium plating from improper graphite anode charging conditions. Furthermore, over-charging the cell can lead to structural collapse of the oxide cathode materials, which also causes the cell to go to a thermal runaway.
With the careful design of the cells and protective components, the risks can be managed and minimized. Comprehensive know-how of cell design, manufacturing processes, and pack components such as a Battery Management System (BMS) is needed for the safe and reliable usage of batteries in every application whether it is small or large.
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