1. Suspension method/climb rate test (direct measurement)
Principle: The wetting rate K is calculated by measuring the change in capillary climb height (ΔH) of the electrolyte in the vertically suspended electrode over time (t) (formula: ΔH = K√t). The larger the value of K, the better the wetting.
Key parameters:
Compacted density: ↑ Compacted density → ↓ Porosity → ↓ K value.
Temperature: Temperature ↑ → Electrolyte viscosity ↓ → K value ↑.
Electrolyte formulation: Low viscosity solvents (such as DMC) or the addition of wetting agents (such as fluorobenzene) can increase the K value.
Applicable scenarios: Rapid screening at the electrode level (e.g., the influence of different compaction densities and current collector types).
2. Cell liquid absorption method (overall assessment)
Principle: Directly measure the mass increment (Δm) of electrolyte absorbed by the cell, and fit Δm/ρA = K√t (where A is the cross-sectional area of the electrode). The shorter the saturation time of electrolyte absorption, the better the wettability.
Advantages: Simple operation, low cost, and direct reflection of cell-level wetting effect.
Application examples:
Membrane type: Ceramic membrane (AlO@PE) has a liquid absorption rate 59% faster than PE membrane due to its higher surface energy.
Injection process: Vacuum injection has a shorter wetting time than atmospheric pressure injection.
3. Ultrasound/CT Imaging (Visual Analysis)
principle:
Ultrasound imaging: Uninfiltrated areas have high impedance and are shown in blue; saturated areas are shown in red.
CT/neutron imaging: tracking electrolyte distribution.
Advantages: Visually displays the uniformity of wetting and identifies dry areas (such as the center of the electrode where wetting dead zones are prone to occur).
4. Electrochemical Impedance Spectroscopy (EIS) and Torque Analysis
principle:
EIS: High-frequency impedance (R) reflects ion transport resistance; R↓ indicates adequate wetting.
Tortuousness (τ): τ = R·κ·A/d (κ is the electrolyte conductivity), a ↓ τ value indicates a smoother ion pathway.
Application: Quantitative assessment of the degree of infiltration.
5. Electrical performance due to poor wetting effect
Capacity decay: Active substances in unwetted areas cannot participate in the reaction.
Increased internal resistance: Poor interface contact leads to an increase in charge transfer impedance (R).
Lithium plating risk: Excessive local current density can cause lithium dendrite formation (common in the central region of thick electrodes).
6. Conclusion
Quantitative assessment should prioritize cell aspiration or EIS tortuosity method, combined with ultrasonic imaging to locate defects. For rapid material screening (e.g., diaphragm, electrolyte), the suspension method can be used. Electrical properties (capacity, internal resistance) should be monitored simultaneously during assessment to verify actual impact.
