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

Abstract

Laboratory-size LiNi 0.8 Co 0.15 Al 0.05 O 2 /graphite lithium-ion pouch cells were cycled over 100% DOD at room temperature and 60°C in order to investigate high-temperature degradation mechanisms of this important technology. Capacity fade for the cell was correlated with that for the individual components, using electrochemical analysis of the electrodes and other diagnostic techniques. The high-temperature cell lost 65% of its initial capacity after 140 cycles at 60 o C compared to only 4% loss for the cell cycled at room temperature. Cell ohmic impedance increased significantly with the elevated temperature cycling, resulting in some of loss of capacity at the C/2 rate. However, as determined with slow rate testing of the individual electrodes, the anode retained most of its original capacity, while the cathode lost 65%, even when cycled with a fresh source of lithium.Diagnostic evaluation of cell components including XRD, Raman, CSAFM and suggest capacity loss occurs primarily due to a rise in the impedance of the cathode, especially at the end-of-charge. The impedance rise may be caused in part by a loss of the conductive carbon at the surface of the cathode and/or by an organic film on the surface of the cathode that becomes non-ionically conductive at low lithium content.

Characterization of high-power lithium-ion cells during constant current cycling

“…The dQ/dV plot for the PG100-1000 showed only one broad peak around 3.9V for charging. The cell with same components cycled 140 times at 60°C with 65% loss of capacity showed a very similar shape [8].…”

“…13, can be attributed either to film formation on the cathode particles or to a break-down of the cathode structure, either through degradation of the oxide or loss of the conductive carbon [8], all of which will lead to isolation of Li-containing cathode material due to high-impedance pathways to parts of the electrode. We can say that most of the capacity fade in these cells comes from the loss of accessible Li sources in the cathode through high-impedance pathways, not from the loss of Li inventory by continuous side reaction.…”

“…The focus of the ATD program is the characterization of the performance of high-power lithium ion cells during calendar life and pulse power cycling with the power profiles developed by PNGV [5,6] and to determine capacity and power fade mechanisms through advanced diagnostics [7]. In support of this effort, the parallel program, Batteries for Advanced Transportation Technologies (BATT) is studying this cell chemistry under constant current cycling regimes with standard test protocols and diagnostic techniques to determine cycle performance and capacity fade mechanisms [8,9].…”

“…In a previous study with LiNi 0.8 Co 0.15 Al 0.05 O 2 /graphite pouch cells, capacity fade during constant current cycling at elevated temperature was examined [8]. Studies included cycling cells at different temperatures, followed by electrochemical, physical and spectroscopic diagnostics on the cell components removed from the cycled cells.…”

Chemomechanics of ionically conductive ceramics for electrical energy conversion and storage

“…In all of these cases, the composition-induced stressfree strains are beyond the failure strains of most brittle materials. As a result, there have been numerous observations of mechanical deformation and battery peformance degradation associated with these shape changes [144][145][146][147][148][149][150][151][152][153]. This electrochemical-cycling-induced fracture has been termed "electrochemical shock," by analogy to thermal shock of brittle materials [13].…”