Diagnostic Characterization of High Power Lithium-Ion Batteries for Use in Hybrid Electric Vehicles

Abstract

A baseline cell chemistry was identified as a carbon anode, LiNi 0.8 Co 0.2 O 2 cathode, and diethyl carbonate-ethylene carbonate LiPF 6 electrolyte, and designed for high power applications. Nine 18650-size advanced technology development cells were tested under a variety of conditions. Selected diagnostic techniques such as synchrotron infrared microscopy, Raman spectroscopy, scanning electronic microscopy, atomic force microscopy, gas chromatography, etc., were used to characterize the anode, cathode, current collectors and electrolyte taken from these cells. The diagnostic results suggest that the four factors that contribute to the cell power loss are solid electrolyte interphase deterioration and nonuniformity on the anode; morphology changes, increase of impedance, and phase separation on the cathode; pitting corrosion on the cathode current collector; and decomposition of the LiPF 6 salt in the electrolyte at elevated temperature.

Electrochemical analysis for cycle performance and capacity fading of a lithium-ion battery cycled at elevated temperature

“…While the cycled anode showed a capacity loss of 10% when compared to a fresh anode, the potential profiles for charging and discharging are almost same to for the two anodes pieces. Previous studies of anode pieces recovered from cycled 18650's showed large film impedance that was removed by continuous cycling and reduction in fresh electrolyte [6]. This behavior was not observed here, probably because any degradation films left on the anode was removed altogether by washing before assembling into the cell with lithium.…”

“…Zhang and co-workers reported that LiPF 6 salt is not stable at elevated temperature and is decomposed to PF 5 (g) and LiF (s). [6] They also observed that electrolyte turned a brown color by the reaction of PF 5 gas and LP40 electrolyte. We also observed a brown stain on the separator after disassembly of cycled cell.…”

“…There are many reasons for capacity fading in lithium battery [6]. During cycling, the fatigue of crystal structure for active materials and the decomposition of electrolyte including solvent and salt will be accelerated at higher temperatures.…”

“…As part of the advanced technology development (ATD) program at the Lawrence Berkeley National Lab. (LBNL), for the development of a high power battery for the hybrid electric vehicle, researchers have developed several diagnostic techniques for the determination of capacity and power fade mechanisms in 18650-size lithium-ion cells during life-cycle pulse testing at temperatures up to 70°C [6]. The high-temperature studies were used primarily as an accelerated aging technique.…”

Cycling performance of low-cost lithium ion batteries with natural graphite and LiFePO4

“…The interest in lithium rechargeable batteries in electric vehicles (EVs) has been significantly increased in recent years [1][2][3]. The important factors for their application are low price, long cycle life, environmental safety, and high specific energy.…”