In situ Raman spectroscopy on silicon nanowire anodes integrated in lithium ion batteries

Rapid decay of silicon anodes during lithiation poses a significant challenge in application of silicon as an anode material in lithium ion batteries. In situ Raman spectroscopy is a powerful method to study the relationship between structural and electrochemical data during electrode cycling and to allow the observation of amorphous as well as liquid and transient species in a battery cell. Herein, we present in situ Raman spectroscopy on high capacity electrode using uncoated and carbon-coated silicon nanowires during first lithiation and delithiation cycle in an optimized lithium ion battery setup and complement the results with operando X-ray reflection diffraction measurements. During lithiation, we were able to detect a new Raman signal at 1859 cm−1 especially on uncoated silicon nanowires. The detailed in situ Raman measurement of the first lithiation/delithiation cycle allowed to differentiate between morphology changes of the electrode as well as interphase formation from electrolyte components

Interplay between wet-dry-cycles and corrosion initiation due to chloride accumulation on AA1050 - A simple experimental approach

Generally aluminum alloys are susceptible to pitting corrosion in chloride containing environments, e. g. in marine climates. A well-known but not well-documented fact is the increasing of chloride concentration over a number of wet-dry cycles which are the outstanding feature of atmospheric corrosion. Moreover, time and frequency of wet-dry cycles and consequently the adsorption of chlorides are quite randomly under natural weathering, complicating the quantification of results. For example reported accumulation rates of chloride from the atmosphere on indoor aluminum surfaces range between 0.01 and 0.13μgcm-2a-1 [1]. In a simple experimental approach the authors simulated a number of natural wet-dry-cycles on an aluminum alloy AA1050. The chloride concentration was monitored by a Cl- -ion sensitive electrode and the electrode potential of the aluminum sample by measurement of the open circuit potential. The choronovoltametric experiments were complemented by FT-IRRAS-technique to investigate the development of oxide films and corrosion products. The deposition of sodium chloride itself cannot be directly detected by IRRAS because NaCl is infrared inactive. However, the influence of chloride ions can be deduced indirectly due to the formation of characteristic corrosion products and the oxide film composition (e.g. occurrence of cadwaladerite). Additionally, owing to the hygroscopic properties of the sodium chloride salt, the amount of adsorbed water is an indication of the salt deposition on the surface. The use of the IRRAS mode allows the study of very thin layers down to less than 1μm. This implies the possibility to detect alteration of the native surface layer before the corrosion attacks emerge. Post experimental microscopic investigation complete the study

In-operando temperature measurement across the interfaces of a lithium-ion battery cell

In this work an experimental setup for in-operando temperature measurements across the interfaces anode - separator/electrolyte - cathode of a lithium-ion battery cell is developed to get a better understanding of the heat generating mechanisms. The results show differences in the heat evolution rates of the anode, the separator and the cathode according to the electrochemical reactions, the state of charge, the overvoltage and the electric current density. The LiCoO2 cathode was identified as the most decisive component for the heat evolution in the investigated battery stack. Changes of the ohmic resistance and the entropy of LiCoO2 with the state of charge were reflected by the temperature measurements