The Effect of Porous Structure of Positive Electrode on Lithium Ion Battery

• Main Authors: Chun-Yen Liu, 劉俊彥
• Other Authors: Chi-Chao Wan
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/33522517894466830985

碩士 === 國立清華大學 === 化學工程學系 === 95 === The effect of rolling positive electrodes into different densities on the performance of lithium ion batteries discharged at different rates was studied by using X-ray diffraction, SEM, AC impedance, cyclic voltammetry, and gravimetrically measured capillary liquid movement. The results show that, as the battery discharged at lower than 1C rate, the capacity increased as electrodes density increased. However, as the discharging rate increased over 2C, the capacity of the densest electrode, 3.6 g/cm3, would drop rapidly. This suggests that rolling positive electrode would make the active particles (LiCoO2) be compacted more closely, resulting in decreased internal impedance and faster kinetics. Therefore, the inter-particle contact quality is the main factor to determine the discharge efficiency if the discharging rate is below 1C. Moreover, as the discharging rate increases over 2C, both liquid ionic conductivity and the contact area between active particles and electrolyte, that is to say “wettability”, would govern the discharge capacity. But, the inter-particle contact quality is still important and the density should be at least denser than 3.2 g/cm3. Namely, these two factors, ionic conductivity and wettability, would become more important for battery discharge at 3C with electrode denser than 3.2 g/cm3.