Modeling separator membranes physical characteristics for optimized lithium ion battery performance

• The effect of the physical characteristics of separators in battery performance is presented.
• The ionic conductivity of the separator depends on the value of the Bruggeman coefficient.
• Bruggeman coefficient is related with the degree of porosity and tortuosity of the membrane.
• The optimal value of the degree of porosity is above 50%.
• The separator thickness should range between 1 μm and 32 μm.

The effect of varying separator membrane physical parameters such as degree of porosity, tortuosity and thickness, on battery delivered capacity was studied in order to optimize performance of lithium-ion batteries. This was achieved by a theoretical mathematical model relating the Bruggeman coefficient with the degree of porosity and tortuosity. The inclusion of the separator membrane in the simulation model of the battery system does not affect the delivered capacity of the battery. The ionic conductivity of the separator and consequently the delivered capacity values obtained at different discharge rates depend on the value of the Bruggeman coefficient, which is related with the degree of porosity and tortuosity of the membrane. Independently of scan rate, the optimal value of the degree of porosity is above 50% and the separator thickness should range between 1 μm and 32 μm for improved battery performance.