Optimization of Inactive Material Content in Lithium Iron Phosphate Electrodes for High Power Applications

The electrochemical performance of lithium iron phosphate (LiFePO₄) electrodes has been studied to find the optimum content of inactive materials (carbon black + polyvinylidene difluoride [PVDF] polymer binder) and to better understand electrode performance with variation in electrode composition. Trade-offs between inactive material content and electrochemical performance have been characterized in terms of electrical resistance, rate-capability, area-specific impedance (ASI), pulse-power characterization, and energy density calculations. The ASI and electrical conductivity were found to correlate well with ohmic polarization. The results showed that a 80:10:10 (active material: binder: carbon agents) electrode had a higher pulse-power density and energy density at rates above 1C as compared to 90:5:5, 86:7:7 and 70:15:15 formulations, while the 70:15:15 electrode had the highest electrical conductivity of 0.79 S cm⁻¹. A CB/PVDF ratio of ca. 1.22 was found to be the optimum formulation of inactive material when the LiFePO₄ composition was 80 wt%.