Cycling capacity fade analysis of 3 Ah high nickel/SiOx-C pouch cells

Abstract

With the development of electric vehicles, higher requirements for battery energy density are put forward. High nickel/SiOx-C batteries with high energy density have become the first choice for long-range electric vehicles. However, high nickel/SiOx-C batteries have the problem of rapid capacity decay in practical use. Non-destructive electrochemical analysis and post-mortem analysis were used to detect the changes in battery capacity and internal resistance during the cycle. The changes in the structure, material morphology and surface composition of positive and negative electrodes before and after the battery cycle were compared, revealing the mechanism of cycling failure of high nickel/SiOx-C batteries. The results show that the capacity decay of the battery presents three stages: the stationary period, the rapid decay period and the extreme decay period. After cycling, the polarization of the battery is more serious, and the polarization internal resistance of the battery, the surface film resistance of the negative electrode and the charge transfer resistance increase significantly. Through differential curve analysis combined with disassembly analysis, it is found that the high nickel cathode material has less attenuation, and the silica carbon anode material has more attenuation and active lithium-ion loss. The expansion and cracking of silicon oxide particles, the loss of negative electrode active material, and the continuous growth of solid electrolyte interface film on the negative electrode surface consuming too much active lithium are the main reasons for the rapid decline of battery capacity.

Keywords

• high nickel/siox-c battery
• capacity fade
• polarization
• post-mortem analysis