Extensive aging analysis of high-power lithium titanate oxide batteries: Impact of the passive electrode effect

Partial electrification of vehicle drive trains, for example by the usage of 48 V systems, require high-powerbatteries with extreme robustness to temperatures, current rates and energy throughputs. In this study, theapplication-relevant lifetime performance of 33 state-of-the-art high-power lithium titanate oxide nickel manganesecobalt oxide (LTO|NMC) cells is measured under cyclic, calendar, and drive cyclic aging regimes. Regularextended check-ups reveal the cell performance in terms of capacity loss and internal resistance increase, whichallows for the identification of critical operating conditions. For the first time a passive electrode effect isidentified in calendar aging tests of LTO cells in which the cathode is geometrically and capacitively oversized.Passive electrode areas lead to a change in cell balancing, which can be illustrated by the shift of the half-cellvoltage curves. Generally, the investigated cells show an excellent cycle stability for shallow cycles, even athigh ambient temperatures and high current rates. Only large cycle depths greater than 70% at elevated temperaturesreduce the battery life significantly. Furthermore, the results show that cells cycled in areas of low stateof charge age faster than in areas of high state of charge. The rise in internal resistance under calendar aging hasthe most detrimental influence on lifetime in a 48 V battery

An investigation of the electrochemical delithiation process of carbon coated α−Fe2O3α-Fe_{2}O_{3} nanoparticles

The electrochemical lithiation–delithiation of iron oxide is a rather complex process, which is still not fully understood. In this study we investigated the electrochemical lithiation–delithiation mechanism of hematite by means of X-ray diffraction (XRD), 57Fe Mössbauer spectroscopy, high-resolution transmission electron microscopy (HRTEM) and X-ray absorption spectroscopy (XAS). Since the delithiation process has been so far less investigated, particular attention was dedicated to the characterization of the chemical species that are formed during this process. The results of this investigation indicated that at the end of the delithiation process lithium iron oxide α-LiFeO2 is formed. The formation of this compound may be the explanation for the irreversible capacity loss in the first cycle, which is usually assigned to the formation of an organic gel-like layer. Based on these results a new charge–discharge mechanism of hematite in lithium-ion batteries (LIBs) is proposed and discussed