Electrolyte Decomposition

 Electrolyte decomposition in a lithium-ion cell can significantly contribute to cell degradation. Several factors can lead to electrolyte decomposition, including voltage limits, operating temperature, overcharging, impurities, electrolyte composition, cell age and cycling

When the electrolyte decomposes, it can lead to the formation of various byproducts, such as gases, solid deposits, and reactive species. These byproducts can negatively impact the performance and stability of the cell in several ways:

• Capacity loss: Electrolyte decomposition can result in the irreversible loss of active lithium ions, reducing the overall capacity of the battery.
• Formation of a passivation layer: Decomposition byproducts can accumulate on the electrode surfaces and form a passivation layer, which increases the resistance to lithium ion transport. This leads to decreased battery performance, including lower energy and power densities.
• Cell impedance increase: The formation of solid deposits or films on the electrode surfaces increases the internal resistance of the cell, leading to higher impedance. This results in reduced power output and increased voltage drop during cell operation.
• Gas evolution and internal pressure increase: Some decomposition reactions generate gases, such as carbon dioxide or carbon monoxide. Accumulation of gas bubbles can cause mechanical stress and increase internal pressure within the cell, potentially leading to cell swelling, leakage, or even rupture.
• Side reactions and electrolyte consumption: Decomposition byproducts may react with electrode materials, resulting in the consumption of active material and reduced electrode performance. Side reactions can also contribute to the growth of unwanted structures, such as dendrites, which can lead to short circuits or internal cell damage.

To mitigate the negative effects of electrolyte decomposition, efforts are made to design electrolytes with improved stability, such as incorporating additives that can suppress decomposition reactions or enhance the formation of a stable solid electrolyte interface (SEI) layer. Controlling operating conditions, such as temperature and voltage limits, is also crucial in minimizing electrolyte decomposition and extending cell lifespan.