Influence of the binder on lithium ion battery electrode tortuosity and performance

The electrochemical performance of porous graphite anodes in lithium ion battery applications is limited by the lithium ion concentration gradients in the liquid electrolyte, especially at high current densities and for thick coatings during battery charging. Beside the electrolyte transport parameters, the porosity and the tortuosity of the coating are key parameters that determine the electrode’s suitability for high power applications. Here, we investigate the tortuosity of graphite anodes using two water as well as three n-methyl-2-pyrrolidone based binder systems by analysis of symmetric cell impedance measurements, demonstrating that tortuosities ranging from ∼3–10 are obtained for graphite anodes of similar thickness (∼100 μm), porosities (∼50%) and areal capacity (∼3.4 mAh/cm²). Furthermore, selected electrodes with tortuosities of 3.1, 4.3, and 10.2 were cycled in cells with reference electrode at charging C-rates from 0.1-20 1/h, illustrating the clear correlation between electrode tortuosity and its rate capability.