Effective Methods to Restore Increased Internal Resistance in Lithium-Ion Battery Packs

Lithium-ion battery packs are widely used in electronics, electric vehicles, and renewable energy systems due to their high energy density and long cycle life. However, over time, internal resistance can rise, leading to reduced performance, slower charging, and shorter runtime. Addressing this issue requires targeted strategies to restore efficiency and extend battery lifespan. Below are scientifically grounded approaches to mitigate increased internal resistance.

1. Balancing Cell Voltages Through Active or Passive Equalization

Uneven cell voltages within a battery pack are a primary cause of elevated internal resistance. When some cells discharge faster than others, stress accumulates, accelerating degradation.

• Passive Equalization: This method uses resistors to dissipate excess energy from overcharged cells, bringing them in line with others. While simple, it generates heat and is less efficient for large packs.

• Active Equalization: Advanced systems redistribute energy between cells using capacitors or inductors, minimizing waste and improving balance. This approach is ideal for high-capacity packs requiring precision.

Implementing regular equalization cycles, especially after deep discharges or prolonged storage, helps maintain uniform cell health and reduces resistance buildup.

2. Optimizing Charging Protocols to Reduce Stress

Improper charging habits, such as using excessive current or skipping temperature controls, can damage battery chemistry and increase resistance.

• Adjust Charge Current: High charging rates generate heat, accelerating electrolyte decomposition and solid electrolyte interface (SEI) layer growth. Lowering the current to manufacturer-recommended levels minimizes stress.

• Temperature Management: Charging below 0°C or above 45°C strains the battery. Use thermal regulation systems or delay charging until optimal temperatures are reached.

• Avoid Full Charges: Keeping the state of charge (SoC) between 20% and 80% reduces voltage-related stress, preserving electrode structure and lowering resistance.

By fine-tuning charging parameters, users can slow degradation and maintain lower internal resistance over time.

3. Thermal Regulation to Prevent Irreversible Damage

Heat is a major contributor to resistance increases, as it degrades electrolytes and accelerates side reactions. Effective thermal management is critical.

• Improving Airflow: For portable devices, ensure vents are unobstructed. In electric vehicles, optimize cooling system designs to enhance heat dissipation.

• Using Phase-Change Materials (PCMs): PCMs absorb excess heat during peak operation, maintaining stable temperatures without active cooling.

• Avoiding High-Temperature Environments: Store batteries in cool, dry places away from direct sunlight. Prolonged exposure to heat above 30°C can permanently damage cells.

Consistent thermal control reduces the rate of resistance growth, ensuring consistent performance across cycles.

4. Reconditioning Through Controlled Cycling

Partial discharges followed by controlled charges can sometimes reverse early-stage resistance increases by redistributing ions and breaking down minor SEI layer buildup.

• Discharge to 50% SoC: Lower the battery’s charge to around 50%, then recharge slowly to 80%. Repeat this cycle 3–5 times.

• Avoid Deep Discharges: Never drain the battery below 10% SoC during reconditioning, as this can worsen degradation.

• Monitor Voltage Stability: Use a multimeter to check for voltage drops during discharge. Sudden drops indicate cell imbalance, requiring further equalization.

This method works best for mild resistance issues and should be paired with other strategies for long-term effectiveness.

By combining cell balancing, optimized charging, thermal regulation, and strategic cycling, users can significantly reduce internal resistance in lithium-ion battery packs. These approaches address both physical and chemical causes of degradation, ensuring reliable performance and prolonged service life.