Abstract
Lithium-ion batteries (LIBs) using a LiFePO4 cathode and graphite anode were assembled in coin cell form and subjected to 1000 charge-discharge cycles at 1, 2, and 5 C at 25 °C. The performance degradation of the LIB cells under different C-rates was analyzed by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy. The most severe degradation occurred at 2 C while degradation was mitigated at the highest C-rate of 5 C. EIS data of the equivalent circuit model provided information on the changes in the internal resistance. The charge-transfer resistance within all the cells increased after the cycle test, with the cell cycled at 2 C presenting the greatest increment in the charge-transfer resistance. Agglomerates were observed on the graphite anodes of the cells cycled at 2 and 5 C; these were more abundantly produced in the former cell. The lower degradation of the cell cycled at 5 C was attributed to the lowered capacity utilization of the anode. The larger cell voltage drop caused by the increased C-rate reduced the electrode potential variation allocated to the net electrochemical reactions, contributing to the charge-discharge specific capacity of the cells.
Highlights
Lithium-ion batteries (LIBs) have been extensively used as rechargeable power sources for mobile and automotive products
Cell formation by Cyclic voltammetry (CV) was achieved for the three assembled LIB cells and similar CV curves were observed for all the cells
This decrease in voltage allocation leads to a low capacity utilization of the anode, which in turn decelerates the degradation of the graphite anode of x FOR PEER
Summary
Lithium-ion batteries (LIBs) have been extensively used as rechargeable power sources for mobile and automotive products. Sun et al investigated the charge-discharge cycling performance of commercial LFP/graphite LIBs in the temperature range 25–55 ◦ C, revealing that the degree of capacity fading was influenced by the operating temperature [14]. High temperatures of >50 ◦ C led to performance degradation, such as a decrease in the reversible charge-discharge specific capacity and increase in the charge-transfer resistance (Rct ) within the anode active materials [13,14]. This study assembled LFP/graphite LIB coin cells and implemented 1000 galvanostatic charge-discharge cycles under different C-rates (1, 2, and 5 C) at 25 ◦ C. A performance degradation mechanism of the LFP/graphite LIBs caused by charge-discharge cycling at 1, 2, and 5 C was proposed
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