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May 22 2025Analyze the polarization reaction principles, polarization types and industry solutions to help improve the service life and safety of lithium-ion batteries!
When a lithium-ion battery suddenly shuts down at low temperatures or generates noticeable heat during fast charging, these phenomena are closely related to battery polarization. As a core challenge in the field of rechargeable batteries, polarization not only affects user experience, but also restricts performance breakthroughs in electric vehicles and energy storage systems. This article will deeply analyze this electrochemical phenomenon and provide a systematic solution.
1. What is lithium-ion battery polarization?
The polarization of lithium-ion batteries is essentially the microscopic manifestation of the deviation of electrode reactions from equilibrium. During the charging and discharging process, "energy barriers" are formed on the surfaces of the positive and negative electrodes, resulting in a mismatch between the migration rate of lithium ions and the speed of electron transmission. This is like a sudden congestion on a highway: the accumulation of charge causes a drop in voltage, a surge in heat generation, and ultimately shortens the battery cycle life.
Typical scenario:
Low temperature environment: The rate at which lithium ions are embedded in the graphite negative electrode slows down, triggering a sudden drop in capacity (e.g., a 40% drop in capacity at -20°C).
Fast charging mode: High current density exacerbates concentration polarization, and the battery surface temperature can rise sharply by more than 15°C.
Typical scenario:
Low temperature environment: The rate at which lithium ions are embedded in the graphite negative electrode slows down, triggering a sudden drop in capacity (e.g., a 40% drop in capacity at -20°C).
Fast charging mode: High current density exacerbates concentration polarization, and the battery surface temperature can rise sharply by more than 15°C.
2. Three types of polarization
(1) Ohmic polarization
Causes: electrolyte resistance, electrode material contact resistance, etc.
Features: Linear relationship with current, decreases with increasing temperature.
Case: When a drone is discharged at a high rate, power interruption often occurs due to a sudden increase in the internal resistance of the lithium-ion battery.
(2) Electrochemical polarization
Mechanism: Insufficient insertion/deinsertion rate of lithium ions on the electrode surface.
Features: Excellent performance at low current density.
Case: When an electric vehicle is cold-started at -30℃, the battery management system(BMS) needs to consume additional energy for preheating, resulting in reduced battery life.
Causes: electrolyte resistance, electrode material contact resistance, etc.
Features: Linear relationship with current, decreases with increasing temperature.
Case: When a drone is discharged at a high rate, power interruption often occurs due to a sudden increase in the internal resistance of the lithium-ion battery.
(2) Electrochemical polarization
Mechanism: Insufficient insertion/deinsertion rate of lithium ions on the electrode surface.
Features: Excellent performance at low current density.
Case: When an electric vehicle is cold-started at -30℃, the battery management system(BMS) needs to consume additional energy for preheating, resulting in reduced battery life.
3. Four core factors affecting polarization
(1) Material dimension
Positive electrode material:
When lithium cobalt oxide batteries are charged and discharged at high rates, the lithium ion insertion/deinsertion rate is fast, but a passivation layer (side reaction product) is easily formed on the surface, which aggravates the electrochemical polarization; the lithium ion diffusion rate of lithium iron phosphate batteries decreases significantly at low temperatures (the diffusion coefficient at -20°C is only 1/10 of that at room temperature), resulting in ohmic polarization dominance.
Electrolyte system:
Liquid electrolytes have a significant lithium salt concentration gradient in the electrolyte under high current (such as LiPF₆ decomposition on the electrode surface), and the electrolyte is oxidized/reduced at high temperature or high pressure, generating gas and solid byproducts, increasing the interface impedance; the rigid contact between solid electrolyte and electrode leads to a "dead zone" for lithium ion transmission, and the grain boundary resistance of sulfide electrolyte in the grain boundary effect is more than 10 times the bulk resistance.
Diaphragm technology:
The porosity of the diaphragm directly affects the migration path of lithium ions and the wettability of the electrolyte. The porosity of commercial diaphragms is usually controlled at 35%~45%, balancing ion transmission and structural strength.
(2) Working conditions
Temperature effect:
At low temperature (-20℃), ohmic polarization is dominant, and the surface temperature rises sharply during fast charging (ΔT＞15℃); at high temperature (45℃), electrochemical polarization is significant, and the SOC estimation error is expanded to ±8%.
Current density:
When charging and discharging at 1C, the lithium ion migration rate matches the electron transfer, and the polarization is mainly ohmic polarization (accounting for 60%); when charging and discharging at 5C, concentration polarization is dominant (accounting for 80%), the concentration gradient of positive electrode lithium salt reaches 1:3, and the risk of lithium precipitation increases sharply.
SOC state:
When SOC is high (＞80%), the tendency of lithium metal deposition on the negative electrode surface decreases, but the aging of SEI film is accelerated; when SOC is low (＜20%), the BMS estimation error increases (ΔSOC＞±5%).
(3) Structural design
Pole sheet thickness:
The internal polarization of 200μm thick electrode is significant during fast charging; 80μm thin electrode is suitable for ultra-fast charging scenarios.
Conductive network:
The local current density of the non-carbon coated electrode is concentrated, which causes ohmic polarization; the charge distribution of the carbon coated electrode is uniform, and the polarization is reduced by 40%.
Interface engineering:
The traditional SEI membrane is mainly composed of Li₂CO₃, which has low mechanical strength and is easy to break, resulting in side reaction cycles and large fluctuations in polarization voltage; the artificial SEI membrane lithium fluoride (LiF) enriched layer (thickness 5 nm) improves lithium ion conductivity, inhibits dendrite growth, and improves polarization stability.
(4) Process level
When the coating uniformity deviation exceeds 5%, local uneven distribution of active substances, conductive network defects or electrolyte penetration differences will form on the surface or inside of the electrode, thereby causing local polarization effects and accelerating capacity decay.
Positive electrode material:
When lithium cobalt oxide batteries are charged and discharged at high rates, the lithium ion insertion/deinsertion rate is fast, but a passivation layer (side reaction product) is easily formed on the surface, which aggravates the electrochemical polarization; the lithium ion diffusion rate of lithium iron phosphate batteries decreases significantly at low temperatures (the diffusion coefficient at -20°C is only 1/10 of that at room temperature), resulting in ohmic polarization dominance.
Electrolyte system:
Liquid electrolytes have a significant lithium salt concentration gradient in the electrolyte under high current (such as LiPF₆ decomposition on the electrode surface), and the electrolyte is oxidized/reduced at high temperature or high pressure, generating gas and solid byproducts, increasing the interface impedance; the rigid contact between solid electrolyte and electrode leads to a "dead zone" for lithium ion transmission, and the grain boundary resistance of sulfide electrolyte in the grain boundary effect is more than 10 times the bulk resistance.
Diaphragm technology:
The porosity of the diaphragm directly affects the migration path of lithium ions and the wettability of the electrolyte. The porosity of commercial diaphragms is usually controlled at 35%~45%, balancing ion transmission and structural strength.
(2) Working conditions
Temperature effect:
At low temperature (-20℃), ohmic polarization is dominant, and the surface temperature rises sharply during fast charging (ΔT＞15℃); at high temperature (45℃), electrochemical polarization is significant, and the SOC estimation error is expanded to ±8%.
Current density:
When charging and discharging at 1C, the lithium ion migration rate matches the electron transfer, and the polarization is mainly ohmic polarization (accounting for 60%); when charging and discharging at 5C, concentration polarization is dominant (accounting for 80%), the concentration gradient of positive electrode lithium salt reaches 1:3, and the risk of lithium precipitation increases sharply.
SOC state:
When SOC is high (＞80%), the tendency of lithium metal deposition on the negative electrode surface decreases, but the aging of SEI film is accelerated; when SOC is low (＜20%), the BMS estimation error increases (ΔSOC＞±5%).
(3) Structural design
Pole sheet thickness:
The internal polarization of 200μm thick electrode is significant during fast charging; 80μm thin electrode is suitable for ultra-fast charging scenarios.
Conductive network:
The local current density of the non-carbon coated electrode is concentrated, which causes ohmic polarization; the charge distribution of the carbon coated electrode is uniform, and the polarization is reduced by 40%.
Interface engineering:
The traditional SEI membrane is mainly composed of Li₂CO₃, which has low mechanical strength and is easy to break, resulting in side reaction cycles and large fluctuations in polarization voltage; the artificial SEI membrane lithium fluoride (LiF) enriched layer (thickness 5 nm) improves lithium ion conductivity, inhibits dendrite growth, and improves polarization stability.
(4) Process level
When the coating uniformity deviation exceeds 5%, local uneven distribution of active substances, conductive network defects or electrolyte penetration differences will form on the surface or inside of the electrode, thereby causing local polarization effects and accelerating capacity decay.
4. Strategies to overcome polarization
(1) Material innovation
Graphene composite electrode: Improve conductivity and reduce ohmic polarization (laboratory data: polarization loss is reduced by 45%).
Solid-state battery technology: Use solid electrolyte to eliminate the concentration polarization problem of liquid electrolyte.
(2) Structural design
Electrode porosity: Increase surface area, provide more channels for ion diffusion, and alleviate concentration polarization.
Flow field optimization: Design structured flow field in liquid flow battery to improve mass transfer efficiency and reduce polarization under high current density.
(3) Intelligent management
Segmented charging: The proportion of constant current stage is reduced to 60%, avoiding lithium precipitation at negative electrode.
Thermal management optimization: Maintaining the operating temperature of lithium-ion battery at 25-40℃ can increase the cycle life by 30%.
(4) Process improvement
Electrode coating uniformity: Strictly control manufacturing accuracy to avoid local polarization abnormalities.
Electrolyte recovery technology: In all-vanadium liquid flow battery, polarization is alleviated and electrolyte activity is restored through oxalic acid reduction and electrode exchange.
(5) New technologies
Polarized battery technology: Utilize polarization effect through special design to improve battery efficiency.
Solid-state battery: Use solid electrolyte to reduce ion transmission resistance and fundamentally reduce polarization.
(6) Recycling
Electrolyte regeneration: Chemically reduce or physically mix aged electrolyte to restore its performance, reduce costs and environmental burden.
(7) Daily measures
For ordinary users, the following measures can effectively reduce the impact of polarization:
Avoid extreme charging and discharging: Keep the power in the range of 20%-80% to reduce lithium metal deposition.
Choose an adapter charger: Give priority to the PD fast charging protocol recommended by the manufacturer to avoid the risk of overcharging.
Temperature adaptability use: Preheat the battery before charging in winter and avoid direct sunlight in summer.
Lithium-ion battery polarization is a roadblock to the upgrade of energy storage technology, but this challenge is gradually being overcome through material innovation, process improvement and intelligent management. Both end consumers and lithium-ion battery wholesalers need to have a deep understanding of the polarization mechanism to drive efficiency improvement and cost optimization with technology.
Graphene composite electrode: Improve conductivity and reduce ohmic polarization (laboratory data: polarization loss is reduced by 45%).
Solid-state battery technology: Use solid electrolyte to eliminate the concentration polarization problem of liquid electrolyte.
(2) Structural design
Electrode porosity: Increase surface area, provide more channels for ion diffusion, and alleviate concentration polarization.
Flow field optimization: Design structured flow field in liquid flow battery to improve mass transfer efficiency and reduce polarization under high current density.
(3) Intelligent management
Segmented charging: The proportion of constant current stage is reduced to 60%, avoiding lithium precipitation at negative electrode.
Thermal management optimization: Maintaining the operating temperature of lithium-ion battery at 25-40℃ can increase the cycle life by 30%.
(4) Process improvement
Electrode coating uniformity: Strictly control manufacturing accuracy to avoid local polarization abnormalities.
Electrolyte recovery technology: In all-vanadium liquid flow battery, polarization is alleviated and electrolyte activity is restored through oxalic acid reduction and electrode exchange.
(5) New technologies
Polarized battery technology: Utilize polarization effect through special design to improve battery efficiency.
Solid-state battery: Use solid electrolyte to reduce ion transmission resistance and fundamentally reduce polarization.
(6) Recycling
Electrolyte regeneration: Chemically reduce or physically mix aged electrolyte to restore its performance, reduce costs and environmental burden.
(7) Daily measures
For ordinary users, the following measures can effectively reduce the impact of polarization:
Avoid extreme charging and discharging: Keep the power in the range of 20%-80% to reduce lithium metal deposition.
Choose an adapter charger: Give priority to the PD fast charging protocol recommended by the manufacturer to avoid the risk of overcharging.
Temperature adaptability use: Preheat the battery before charging in winter and avoid direct sunlight in summer.
Lithium-ion battery polarization is a roadblock to the upgrade of energy storage technology, but this challenge is gradually being overcome through material innovation, process improvement and intelligent management. Both end consumers and lithium-ion battery wholesalers need to have a deep understanding of the polarization mechanism to drive efficiency improvement and cost optimization with technology.
