Aging Mechanisms of Ultra-High-Rate Lithium-Ion Batteries for Electromagnetic Launch

Abstract

We demonstrate the aging mechanisms of ultra-high-rate lithium iron phosphate (LiFePO[Formula: see text]/graphite batteries for electromagnetic launch (EML) applications. These lithium-ion batteries (LIBs) are repetitively charged at a rate of 1[Formula: see text]C and discharged at a rate of 70[Formula: see text]C for 300 times. After 300 cycles, the capacity retention is 79.9%, and the internal resistance rises from 1.4[Formula: see text]m[Formula: see text] to 2.4[Formula: see text]m[Formula: see text]. The scanning electron microscopy (SEM) results show that the surface of the anode presents an absolutely different morphology after 300 cycles, indicating the occurrence of severe secondary reactions. The X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS) results reveal that part of LiFePO4 is replaced by FePO4 in the cathode of fully discharged LIBs during repetitive cycling, meaning the occurrence of loss of active lithium. Moreover, the Fourier transform infrared spectroscopy (FTIR) and XPS results display that the surface of the anode is coated by a layer of compounds including Li2CO3, ROCO2Li and LiF after 300 cycles, which is the cause of loss of active lithium and results in the decline of capacity. As the first research about the aging mechanisms of ultra-high-rate LiFePO4/graphite batteries, this work brings comprehension of the degradation of EML-used LIBs, which is of great significance to EML technology.