Carbon nanostructures modified LiFePO4 cathodes for lithium ion battery applications: Optimized porosity and composition

Lithium iron phosphate (LiFePO₄) battery cathode was fabricated without using any metallic current collector and polymeric binder. Carbon nanostructures (CNS) were used as microbinders for LiFePO4 particles and at the same time as a 3Dcurrent collector. Afacile and cost effective method of fabricating composite cathodes of CNS and LiFePO4 was developed. Thick electrodes with high loading of active material (20-25 mg cm^-2) were obtained that are almost 2-3 folds higher than commercial electrodes. SEM images confirm that the 3D CNS conductive network encapsulated the LiFePO4 particles homogenously facilitating the charge transfer at the electrode-CNS interface. The composition, scan rate and porosity of the paper-like cathode were sequentially varied and their influence was systematically monitored by means of linear sweep cyclic voltammetry and ACelectrochemical impedance spectroscopy. Addition of CNS improved the electrode's bulk electronic conductivity, mechanical integrity, surface area and double layer capacitance, yet compromised the charge transfer resistance at the electrode-electrolyte interface. Based on a range of the tested binder-free electrodes, this study proposes that electrodes with 20 wt% CNS having 49±2.5% porosity had realized best improvements of two folds and four folds in the electronic conductivity and diffusion coefficient, respectively.