Mesoscale Modeling of a Li-Ion Polymer Cell

Finite element models of a three-dimensional, porous cathode were constructed and analyzed by the COMSOL multiphysics package ͑version 3.2͒.Four types of cathode active material particles, arranged in both regular and random arrays, were modeled.Experimental studies of Li/PEO-LiClO 4 /Li 1+x Mn 2 O 4 ͑where 0 Ͻ x Ͻ 1͒ were used to validate simulation results.Two parameters, Li ion diffusivity into Li 1+x Mn 2 O 4 particles, and contact resistance at the interface between cathode particles and the current collector, were obtained by curve-fitting discharge curves of simulation results of regular array models, with Li 1+x Mn 2 O 4 particles ͑3.6 m͒ with experimental results.Diffusivities of Li ions were found to be 4 ϫ 10 -13 , 6 ϫ 10 -13 , 1 ϫ 10 -12 , and 5 ϫ 10 -12 cm 2 /s for Li 1+x Mn 2 O 4 particles sintered at 800, 600, 500, and 450°C, respectively.Contact resistances were found to be 3.5 ⍀ cm 2 for Li 1+x Mn 2 O 4 particles prepared at 600 and 800°C, and 10.5 ⍀ cm 2 for particles prepared at 450 and 500°C.Regular arrays were shown to increase achievable capacity from 5 to 50% of the theoretical capacity, compared with random arrays, at C/10 for samples sintered at 500°C.Smaller particle sizes of active material particles were also shown to be beneficial for high power density applications and for low diffusivity active materials.