Comparative Analysis of Stacking vs. Winding Processes in Lithium Battery Manufacturing

1. Process Principles

Stacking Process:

Anode and cathode sheets are cut to specified dimensions, then laminated with separators to form unit cells. These unit cells are stacked in parallel to create battery modules.

Winding Process:

Pre-cut anode sheets, separators, and cathode sheets are wound in a defined sequence around a fixed mandrel, compressed into cylindrical, elliptical, or prismatic shapes. The winding electrodes are then housed in cylindrical or prismatic metal casings. Electrode dimensions and winding turns are determined by the battery's design capacity.

2. Electrochemical Performance Comparison

Stacking cells exhibit lower internal resistance due to parallel welding of multiple tabs, shortening lithium-ion migration paths. This reduces heat generation during operation and slows initial energy density degradation. In contrast, winding cells rely on single-tab current output, resulting in higher internal resistance.

Cycle Life:

Stacking cells demonstrate superior thermal management, enabling uniform heat distribution. Winding cells exhibit gradient structural and mechanical properties, leading to uneven heat dissipation and localized temperature gradients. This accelerates capacity fade and reduces cycle life in wound cells.

Electrode Mechanical Stress:

Stacking electrodes experience uniform mechanical stress without localized concentration, minimizing material layer damage during charge/discharge cycles. Winding cells develop stress concentrations at bending points, increasing risks of structural failure, short circuits, and lithium plating under electrical load.

Rate Capability:

Stacking cells achieve enhanced rate performance due to parallelized current pathways from multiple electrode layers, enabling faster high-current discharge. Winding cells face limitations from single-tab architecture.

Energy Density Design:

Stacking optimizes packaging space utilization, maximizing active material loading for higher energy density. Winding cells suffer from space inefficiency due to curved electrode geometry and dual-layer separator configurations.

3. Process Advantages

Stacking Process:

• High Volumetric Capacity: Superior space utilization enables higher capacity within equivalent volumes.
• Elevated Energy Density: Higher discharge voltage plateau and volumetric capacity.
• Design Flexibility: Customizable electrode dimensions support non-standard cell geometries.

Winding Process:

• Simplified Spot Welding: Requires only two welding points per cell.
• Production Scalability: Simplified two-electrode configuration streamlines process control.
• Efficient Slitting: Single anode/cathode slitting operation reduces defect rates.

4. Process Limitations

Stacking Process:

• Cold Welding Risks: Multi-tab lamination increases susceptibility to incomplete welds.
• Low Equipment Efficiency: Domestic stacking machines operate at 0.8 sec/layer vs. 0.17 sec/layer for imported counterparts.

Winding Process:

• High Polarization Losses: Single-tab design exacerbates internal polarization, degrading rate performance.
• Thermal Management Challenges: Difficulty implementing inter-cell thermal isolation increases thermal runaway risks.
• Thickness Variability: Structural inhomogeneity causes uneven thickness at tabs, separator edges, and cell sides.

5. Conclusion

Stacking and winding processes present distinct trade-offs in lithium battery manufacturing. Stacking excels in energy density, thermal performance, and design flexibility, making it ideal for new energy vehicles and energy storage systems. Winding offers cost efficiency and scalability advantages for high-volume applications like consumer electronics. Continuous technological advancements will further optimize both methodologies, driving innovation across the lithium battery industry.

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