Modeling Salt Polarization and Precipitation in High Loading Anodes during Cold Fast Charge
Cold fast charging high-loading anodes induces salt depletion and solid-phase precipitation, requiring coupled transport modeling to prevent lithium plating.
Macmullin Factor
Meaning
A dimensionless ratio that compares the effective resistivity of a porous medium filled with electrolyte to the bulk resistivity of the electrolyte itself describes the transport resistance introduced by a separator or electrode. In cell development, the macmullin factor quantifies the tortuosity and porosity of the separator membrane. Sourcing engineers utilize this metric to compare membranes from different suppliers because a high value indicates restricted ion transport and lower high-rate discharge performance.
This parameter isolates the physical structure of the porous separator from the chemistry of the electrolyte.
Transport Resistance
Ion migration through a separator is always slower than in free solution due to the physical barriers of the polymer matrix. A high macmullin factor means the ions must follow a longer and more complex pathway through the pores. This increased path length raises the internal resistance of the cell, especially at high current densities.
Structural Feature
Porosity and tortuosity together determine this transport variable. The macmullin factor decreases as porosity increases, but mechanical strength considerations limit how porous a separator can be manufactured. Balance between mechanical durability and electrochemical transport is achieved by selecting an optimal pore structure.
Quality Assessment
Inconsistent separator material leads to localized hot spots and uneven current distributions during cell operation. Measuring the macmullin factor across different batches allows quality control teams to verify the uniformity of incoming membrane rolls. This test is a standard part of the supplier qualification protocol.