Accelerated aging and degradation mechanism of LiFePO₄/graphite batteries cycled at high discharge rates

Abstract

The effects of discharge rates (0.5C, 1.0C, 2.0C, 3.0C, 4.0C and 5.0C) on the aging of LiFePO 4 /graphite full cells are researched by disassembling the fresh and aged full cells. The capacity degradation mechanism is analyzed via electrochemical performance, surface morphologies and compositions, and the structure of the anode and cathode electrodes. The capacity fade is accelerated with increasing discharge rates. The irreversible loss of active lithium due to the generation of an SEI film is the primary aging factor for the full cells cycled at low discharge rates. However, when the discharge rate is greater than or equal to 4.0C, the performance degradation of the LiFePO 4 electrode is distinct due to structure decay, which is caused by quick and repeated intercalation of lithium ions and elevated temperature during discharging.In addition, the SEI film on the anode tends to be unstable after the rapid extraction of lithium ions at high discharge rates, and this enhances the loss of active lithium. Therefore, it is indicated that the degradation mechanism is changed for the full cells aged at 4.0C and 5.0C. Besides, the high discharge rate also increases the internal resistance of the full cell, which is detrimental to high rate discharge performance.

Estimating the State of Health of Lithium-Ion Batteries with a High Discharge Rate through Impedance

“…Many studies have shown that a higher discharge rate can accelerate battery aging [28][29][30]. Several hypotheses have been made to explain this phenomenon.…”

Aging model development based on multidisciplinary parameters for lithium‐ion batteries

“…However, it will decrease with the cycle numbers rising, that is, battery aging effects. For example, the battery capacity will drop down, internal resistance will increase and the chemical reaction rate will become slow . Such consequences caused by aging process of batteries are the main reason for the drop of operating performance of large pored electrical machines and limit the development of equipment which applies batteries as the energy storage system.…”

“…), some researches claim that the change of internal structure is a vital factor leads to the variety of batteries capacity . In Chikashi et al's research, the deposition of solid electrolyte interphase (SEI) on electrodes surface declines the capacity and cyclic performance of lithium‐ion batteries . Alex et al and Vadim et al studies indicate that the decomposition of electrolytes accelerates the aging process of lithium‐ion batteries owing to the falling number of active substances in electrolytes .…”

“…For example, the battery capacity will drop down, internal resistance will increase and the chemical reaction rate will become slow. [1][2][3] Such consequences caused by aging process of batteries are the main reason for the drop of operating performance of large pored electrical machines and limit the development of equipment which applies batteries as the energy storage system. Thus, it is important to predict the aging process, and the remaining useful lifetime (RUL) of lithium-ions batteries.…”

“…[4][5][6][7] In Chikashi et al's research, the deposition of solid electrolyte interphase (SEI) on electrodes surface declines the capacity and cyclic performance of lithium-ion batteries. 2,7 Alex et al and Vadim et al studies indicate that the decomposition of electrolytes accelerates the aging process of lithium-ion batteries owing to the falling number of active substances in electrolytes. 8,9 Furthermore, Prasant et al studied capacity fading and voltage decay upon cycling, according to the results, the capacity fading is effectively prevented, and the internal resistance changed a little when the cathode rich in lithium and manganese is added a bit of aluminium.…”