Electrode Assembly Undercoat Layer Short-Circuit Suppression

An undercoat layer is introduced as an intermediary between the positive electrode active material layer and the positive electrode current collector. This undercoat layer extends beyond the edge of the positive electrode active material layer to provide a buffer zone that prevents direct contact between the negative electrode active material layer and the positive electrode current collector, while maintaining electrical conductivity through the use of conductive materials or treatments in the undercoat layer.

The undercoat layer is applied with spatially varying properties: in the region overlapping with the positive electrode active material layer, it provides electrical conductivity for normal operation, while in the peripheral region extending beyond the active material layer edge, it provides enhanced insulation and mechanical buffer properties to prevent short-circuits. This local differentiation of properties allows simultaneous achievement of conductivity and short-circuit prevention.

The undercoat layer serves multiple functions simultaneously: it provides electrical conductivity for normal charge-discharge operations, acts as a mechanical buffer to prevent direct contact between electrodes, and provides thermal stability. By combining these functions in a single layer rather than adding separate insulating layers, the solution improves safety without significantly increasing production complexity or inhibiting ionic conductivity.

The resistance value of the undercoat layer is optimized to fall within a specific range that balances conductivity and insulation properties. By controlling the resistance parameter within this optimal range, the undercoat layer maintains sufficient electrical conductivity for normal operation while providing adequate insulation to prevent short-circuits, thereby improving safety without requiring additional insulating layers that would complicate production.