Abstract
Alongside electrical loads, it is known that temperature has a strong influence on battery behavior and lifetime. Investigations have mainly been performed at homogeneous temperatures and non-homogeneous conditions in single cells have at best been simulated. This publication presents the development of a methodology and experimental setup to investigate the influence of thermal boundary conditions during the operation of lithium-ion cells. In particular, spatially inhomogeneous and transient thermal boundary conditions and periodical electrical cycles were superimposed in different combinations. This required a thorough design of the thermal boundary conditions applied to the cells. Unlike in other contributions that rely on placing cells in a climatic chamber to control ambient air temperature, here the cell surfaces and tabs were directly connected to individual cooling and heating plates. This improves the control of the cells’ internal temperature, even with high currents accompanied by strong internal heat dissipation. The aging process over a large number of electrical cycles is presented by means of discharge capacity and impedance spectra determined in repeated intermediate characterizations. The influence of spatial temperature gradients and temporal temperature changes on the cyclic degradation is revealed. It appears that the overall temperature level is indeed a decisive parameter for capacity fade during cyclic aging, while the intensity of a temperature gradient is not as essential. Furthermore, temperature changes can have a substantial impact and potentially lead to stronger degradation than spatial inhomogeneities.
Highlights
It is well known that both the operation [1] and the aging [2,3] of lithium-ion cells highly depend on temperature
The 24 cells were exposed to 50 full cycles at 1C and a temperature of 25 °C prior to the begin of life (BoL) characterization of the study with measurements of the electrochemical impedance being performed at -50, -20, -10, and 0 cycles
It can be stated that higher gradients do not necessarily lead to accelerated aging, but rather the overall temperature level of the cell is of greater relevance
Summary
It is well known that both the operation [1] and the aging [2,3] of lithium-ion cells highly depend on temperature. This dependency originates from the temperature-dependent material properties [4]. The increasing utilization of lithium-ion cells in the automotive industry is accompanied by the application of thermal management systems to maintain performance and ensure secure operation. The heat transfer promoted by thermal management systems inevitably induces temperature gradients [13,14,15], which directly affect the temporal and spatial temperature distribution in the cells. Carter et al [17] and Atkinson et al [18] showed the effect of small-scale temperature gradients on the performance and degradation
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