Monitoring the Formation of Nickel-Poor and Nickel-Rich Oxide Cathode Materials for Lithium-Ion Batteries with Synchrotron Radiation.

The syntheses of Ni-poor (NCM111, LiNi1/3Co1/3Mn1/3O2) and Ni-rich (NCM811 LiNi0.8Co0.1Mn0.1O2) lithium transition-metal oxides (space group R3̅m) from hydroxide precursors (Ni1/3Co1/3Mn1/3(OH)2, Ni0.8Co0.1Mn0.1(OH)2) are investigated using in situ synchrotron powder diffraction and near-edge X-ray absorption fine structure spectroscopy. The development of the layered structure of these two cathode materials proceeds via two utterly different reaction mechanisms. While the synthesis of NCM811 involves a rock salt-type intermediate phase, NCM111 reveals a layered structure throughout the entire synthesis. Moreover, the necessity and the impact of a preannealing step and a high-temperature holding step are discussed.

In-situ Electrochemical X-ray Diffraction: A Rigorous Method to Navigate within Phase Diagrams Reveals ß-Fe1+x Se as Superconductor for All x.

We report the precise postsynthetic control of the composition of ß-Fe1+x Se by electrochemistry with simultaneous tracking of the associated structural changes via in situ synchrotron X-ray diffraction. We access the full phase width of 0.01

Challenges Considering the Degradation of Cell Components in Commercial Lithium-Ion Cells: A Review and Evaluation of Present Systems.

Owing to the high energy and power density of lithium-ion cells (1200 Wh kg-1 and 200 Wh kg-1) and due to their compact design, they are used as energy storage devices in many contemporary mobile applications such as telecommunication systems, notebooks and domestic appliances. Meanwhile their application is not limited only to consumer electronics, they are also standard in hybrid electric (HEVs) and electric vehicles (EVs). However, the profitable application of lithium-ion cells in the automobile industry requires lower costs, lower safety risks, a higher specific energy density and a longer lifetime under everyday conditions. All these aspects are directly or indirectly related to the degradation of the materials in a lithium-ion cell. One possibility for reducing the costs is a second life application of the cells after their usage in (H)EVs. In order to enable this, the safety risks at the end of life of a cell operated in a vehicle have to be reliably predicted. This requires a fundamental knowledge about underlying material degradations during operation. The safety risk of a lithium-ion cell increases during operation because the voltage windows in which the electrodes are cycled shift, resulting in a higher possibility that at least one electrode is operated in a meta- or unstable state. Furthermore, higher impedances due to material degradations lead to increasing heat generation and therefore to an increase in the risk of failure. Higher energy densities can be achieved by raising the end of charge voltage of a cell, causing additional safety risks because many cathode materials tend to decompose at high voltages. Another possibility for achieving higher energy densities is to use nickel-rich or lithium-excess cathode materials, since cathodes are currently limiting the capacity of lithium-ion cells. But these systems show a poor cycling stability (a higher degradation rate). The lifetime of a lithium-ion cell is limited by the degradation of the individual cell components. Although the degradation of materials is the key consideration in achieving lower costs, a higher safety standard, higher energy densities and a longer lifetime, the degradation of the individual cell components in dependence on the operation conditions has hardly been investigated and is poorly understood. The present work reviews known material degradations in commercial lithium-ion cells, shows a way to analyze such degradations in dependence on the operation conditions and describes how these degradation processes lead to observed performance drops.

Unraveling the Degradation Process of LiNi0.8Co0.15Al0.05O2 Electrodes in Commercial Lithium Ion Batteries by Electronic Structure Investigations.

The degradation of LiNi0.8Co0.15Al0.05O2 (LNCAO) is reflected by the electrochemical performance in the fatigued state and correlated with the redox behavior of these cathodes. The detailed electrochemical performance of these samples is investigated by galvanostatic and voltammetric cycling as well as with the galvanostatic intermittent titration technique (GITT). Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to investigate the oxidation state of all three materials at the Ni L2,3, O K, and Co L2,3 edges at five different states of charge. Surface and more bulklike properties are distinguished by total electron yield (TEY) and fluorescence yield (FY) measurements. The electrochemical investigations revealed that the changes in the cell performance of the differently aged materials can be explained by considering the reaction kinetics of the intercalation/deintercalation process. The failure of the redox process of oxygen and nickel at low voltages leads to a significant decrease of the reaction rates in the fatigued cathodes. The accompanied cyclic voltammogram (CV) peaks appear as two peaks because of the local minimum of the reaction rate, although it is one peak in the CV of the calendarically aged LNCAO. The absence of the oxidation/reduction process at low voltages can be traced back to changes in the surface morphology (formation of a NiO-like structure). Further consequences of these material changes are overpotentials, which lead to capacity losses of up to 30% (cycled with a C/3 rate).