Why does the lithium-ion battery anode have an extra layer compared to the cathode?

An excessively thick anode prevents lithium dendrite formation

1. To meet the requirements of structural safety and capacity matching, the anode sheet must completely envelop the cathode sheet when positioned as the outer layer during the stacking process. This prevents the cathode edges from coming into direct contact with the electrolyte, which could trigger lithium plating. The anode must provide sufficient coverage (overhang) over the cathode. The design with an extra layer ensures that all cathode sheets are fully enclosed by the anode, thereby preventing localized lithium dendrite growth.

Anode Expansion: Multi-Layer Protection for Cell Safety

2. Expansion Compensation and Mechanical Stability: Anode materials (such as graphite) expand during lithium insertion. An additional layer of anode provides physical buffer space, reducing internal stress in the cell caused by expansion. Additionally, since anode materials have good plastic deformation capabilities, the outer anode layer optimizes the overall structural strength of the cell.

Imbalance Between Anode and Cathode Sheets: Significant Battery Risks

3. If the number of cathode sheets exceeds that of anode sheets, the following consequences may occur: Capacity imbalance and lithium deposition: If the active area of the cathode is not fully covered by the anode (imbalanced N/P ratio), lithium ions cannot be effectively charged and discharged, leading to dendrite formation. This can puncture the separator and cause a short circuit. Cycle degradation and safety hazards: Under these conditions, the battery’s internal resistance increases, coulombic efficiency plummets, and issues such as gas generation and swelling arise; in severe cases, this can trigger thermal runaway.

Anode optimization and cathode reduction: A new era for batteries

4. Conclusion: Adding an extra layer of anode material is a key design strategy for optimizing electrochemical performance and safety, whereas an excess of cathode material directly threatens battery lifespan and safety.