Battery polarization in lithium-ion batteries refers to the internal voltage losses that occur when a battery is charged or discharged. This loss is due to various factors, leading to a difference between the battery's open-circuit voltage (the voltage when no current is flowing) and the operational voltage when the battery is under load or being charged.
✔️There are three main types of polarization:
1. Ohmic Polarization:
In a battery, when electrical current flows, there's resistance. This resistance is mainly due to the various components of the battery, such as the electrodes, separator, and electrolyte. This causes a drop in voltage, thereby causing the battery to lose some of its efficiency. The following crucial components of the cell contribute to this resistance.
Electrode Resistance: The materials used for electrodes, while good conductors, aren't perfect. Their inherent resistance can cause voltage drops.
Electrolyte Resistance: The medium through which ions travel, the electrolyte, also offers resistance. Its nature, thickness, and temperature can influence how much resistance it offers to ion flow.
Separator Resistance: The separator, which ensures the positive and negative electrodes don’t come into direct contact, can add to the resistance, especially if it gets clogged or compromised.
2. Concentration Polarization:
Concentration polarization is the result of following phenomena:
Ion Movement: As a battery discharges, lithium ions travel from the anode to the cathode. This movement creates a difference in ion concentrations between the surface of the electrode and its interior, a phenomenon known as a concentration gradient.
Saturation Points: If an electrode becomes saturated with ions, it can't accept any more. This can create an "ion traffic jam," leading to more pronounced concentration gradients and higher resistance.
3. Electrochemical Polarization:
Reaction Kinetics: Electrochemical reactions involve intricate steps, including the adsorption of ions onto electrode surfaces, the breaking/forming of chemical bonds, and desorption. The speed of these steps can limit the overall rate of the reaction.
Activation Energy: Some reactions require an energy threshold to commence. If the energy provided is just on the cusp of this threshold, the reactions might be slower, leading to polarization.
Electrode Surface Characteristics: The surface of an electrode plays a critical role in determining how efficiently reactions take place. Surface imperfections, contamination, or degradation can hamper the smooth progression of electrochemical reactions.
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