Optimizing Lithium Battery Busbar Geometry for Current Density: 7 Key Factors

Why Busbar Geometry Matters in Lithium Battery Design

Busbars are essential for efficient current distribution in lithium-ion battery packs used in EVs and energy storage systems. Optimizing their geometry (width, length, and thickness) ensures low resistance, minimal heat generation, and maximum safety.

Quick Answer:

To optimize busbar geometry for current density:
✅ Choose the right material – Copper for high conductivity, aluminum for cost savings.
✅ Match width to cell terminals – About ¾ of the terminal width for optimal contact.
✅ Select thickness based on ampacity – Use 1/8” copper for ~150 A, ensuring low resistance.
✅ Consider heat dissipation – Thick busbars reduce heat, while cooling systems may be needed for high-power applications.

This guide breaks down 7 key factors to help engineers, DIY builders, and battery designers create efficient and safe busbar designs.

1. Determining Current Requirements for Busbars

Why It Matters:

The first step in busbar design is defining continuous and short-circuit current requirements. The busbar must handle these currents without excessive heating or voltage drops.

Example Calculation:

Consider a battery pack with 9 cells in series, each 50 Ah with a 3C discharge rate:

• Continuous Current: 50 Ah × 3C = 150 A
• Short-Circuit Current: Determined using Ohm’s Law with internal resistance
  • If each cell has 2 mΩ resistance, the total pack resistance (9 cells) is 18 mΩ.
  • With a 32.85V pack voltage, the short-circuit current = 1825 A (32.85V / 0.018Ω).

Design Tip: Busbars should be optimized primarily for continuous current, while safety components (fuses, circuit breakers) handle short-circuit events.

2. Selecting the Right Busbar Material

Copper vs. Aluminum: Pros & Cons

Best Practice:

• Use copper for high-power applications (EVs, grid storage).
• Use aluminum for cost savings, but ensure proper terminal connections to avoid galvanic corrosion.

3. Optimizing Busbar Width for Efficient Current Flow

Key Principle:

• The busbar width should match at least ¾ of the cell terminal width to maximize electrical contact and minimize resistance.

Example Design:

For a ¾” diameter cell terminal, use a ¾” wide busbar for optimal connectivity.

Why It Matters:

• Too narrow? Increases resistance, leading to heat buildup.
• Too wide? Adds unnecessary weight and cost.

 

4. Choosing the Right Busbar Thickness Based on Ampacity

Formula for Resistance:

R=Aρ×l​​

Where:

• $R$ = Resistance
• $\rho$ = Material resistivity
• $l$ = Length
• $A$ = Cross-sectional area (width × thickness)

Ampacity Chart (Copper, ¾” Wide, 30°C Rise)

Example Selection:

• For 150 A continuous current, 1/8” thick copper is recommended (215 A ampacity, leaving a safety margin).
• If using aluminum, increase thickness by 40% to compensate for lower conductivity.

5. Managing Heat Dissipation to Prevent Overheating

Why It Matters:

• High current densities generate heat, which reduces efficiency and can cause failure.
• Poor heat dissipation accelerates battery degradation.

Solutions:

✅ Use thicker busbars to reduce resistance.
✅ Ensure airflow around busbars or add liquid cooling for high-power systems.
✅ Check connection tightness – loose connections increase resistance and heat.

6. Ensuring Secure Mechanical Attachment & Safety Measures

Why It’s Important:

Loose busbars cause:
❌ Higher contact resistance → Increased heat & inefficiency
❌ Potential short circuits → Safety hazards

Best Practices:

✅ Use proper fastening techniques (bolts, compression fittings).
✅ Check tightness regularly – especially in vibrating environments (EVs).
✅ Include fuses/circuit breakers to protect against short-circuit currents.

 

7. Practical Example: Optimized Busbar Design for an 8s2p Battery Pack

Scenario:

• 8 cells in series, 2 in parallel → 320 Ah total capacity
• 150 A continuous current (with 300 A ANL fuse)

Recommended Busbar Design:

Conclusion: Key Takeaways for Busbar Optimization

🔋 To optimize lithium battery busbars for current density:
✅ Choose copper for best performance, or aluminum for cost savings.
✅ Match busbar width to at least ¾ of cell terminal size.
✅ Use ampacity charts – 1/8” copper handles ~150 A safely.
✅ Ensure secure attachment to minimize resistance and heat buildup.
✅ Implement thermal management for long-term battery health.