In lithium battery PACK design, compression bars (fixing strips) play a critical mechanical role, but they also have a direct and long-term impact on the internal resistance of the battery pack. At EverExceed, this factor is fully considered in the design of lithium battery solutions for energy storage systems, UPS backup power, and industrial applications.
This is the most direct and critical impact. The primary function of compression bars is to apply uniform and stable pressure to fix multiple cells into an integrated lithium battery module.
Pressure uniformity:
Under ideal conditions, compression bars work together with end plates to apply appropriate and evenly distributed pressure at the connection points between the battery terminals (positive and negative poles) and the busbars.
Proper pressure can:
Reduce contact resistance: Tight contact increases the effective contact area between the terminals and busbars, significantly lowering contact resistance, which is a major contributor to the total PACK internal resistance.
Ensure mechanical stability: Stable pressure prevents loosening of connections under vibration, thermal expansion, and other harsh operating conditions. Loose connections can sharply increase contact resistance and may even cause arcing or localized overheating.
Consequences of insufficient or excessive pressure:
Insufficient pressure: Poor contact leads to a noticeable increase in contact resistance, causing excessive heat generation, reduced energy efficiency, and increased risk of thermal runaway.
Excessive pressure: Over-compression may damage cell casings or terminals, resulting in performance degradation or internal short circuits, posing serious safety risks.
In lithium battery modules where multiple cells are connected in parallel, uniform current distribution is essential.
If compression bar pressure is uneven, some cells will exhibit higher contact resistance at the busbar interface. As a result, current preferentially flows through paths with lower resistance.
This causes:
Uneven current sharing among cells
Certain cells operating at higher effective C-rates than designed
Accelerated aging of overstressed cells
At the PACK level, this imbalance manifests as increased and uneven internal resistance, reducing available capacity and power output.
Internal resistance generates Joule heat according to the equation:
Q = I²R
An increase in contact resistance leads to additional localized heat at connection points.
The design and material selection of compression bars (e.g., use of thermally conductive materials or integration with cooling systems) directly affect heat dissipation pathways. Well-designed structures help remove heat efficiently and maintain stable operating temperatures at critical electrical joints.
Temperature effect on metal resistivity:
Busbars and terminals (typically copper or aluminum) experience increased resistivity as temperature rises. Effective thermal management limits temperature rise and helps suppress resistance growth.
The ability of the compression bar system to resist vibration, creep, and stress relaxation determines whether stable pressure can be maintained throughout the battery lifecycle.
If pressure decays over time due to material fatigue or improper mechanical design, contact resistance will gradually increase. This leads to abnormal growth of PACK internal resistance during cycling or long-term operation, accelerating performance degradation and shortening service life.
| Impact Area | Mechanism Affecting Internal Resistance | Possible Consequences |
|---|---|---|
| Contact pressure | Directly determines contact resistance between terminals and busbars; proper pressure minimizes resistance | Uneven pressure increases total internal resistance, causing heat and efficiency loss |
| Mechanical stability | Prevents loosening under vibration and load variation | Unstable internal resistance, risk of voltage spikes and arcing |
| Current distribution | Affects current sharing among parallel cells | Reduced capacity and power, accelerated localized aging |
| Thermal management | Influences heat dissipation and metal resistivity | High temperature further increases resistance, forming a thermal-resistance loop |
| Long-term reliability | Determines long-term stability of contact resistance | Abnormal resistance growth and reduced battery lifespan |
At EverExceed, compression bar structures, busbar design, and cell fixation methods are carefully optimized to ensure low contact resistance, uniform current distribution, excellent thermal performance, and long-term reliability. This engineering philosophy is applied across our lithium battery PACKs for energy storage systems, UPS backup power, data centers, and industrial power solutions, ensuring stable internal resistance and extended service life throughout the product lifecycle.
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