Alex Friesen

Self-Healing Wide and Thin Li Metal Anodes Prepared Using Calendared Li Metal Powder for Improving Cycle Life and Rate Capability

The commercialization of Li metal electrodes is a long-standing objective in the battery community. To accomplish this goal, the formation of Li dendrites and mossy Li deposition, which cause poor cycle performance and safety issues, must be resolved. In addition, it is necessary to develop wide and thin Li metal anodes to increase not only the energy density, but also the design freedom of large-scale Li-metal-based batteries. We solved both issues by developing a novel approach involving the application of calendared stabilized Li metal powder (LiMP) electrodes as anodes. In this study, we fabricated a 21.5 cm wide and 40 μm thick compressed LiMP electrode and investigated the correlation between the compression level and electrochemical performance. A high level of compression (40% compression) physically activated the LiMP surface to suppress the dendritic and mossy Li metal formation at high current densities. Furthermore, as a result of the LiMP self-healing because of electrochemical activation, the 40% compressed LiMP electrode exhibited an excellent cycle performance (reaching 90% of the initial discharge capacity after the 360th cycle), which was improved by more than a factor of 2 compared to that of a flat Li metal foil with the same thickness (90% of the initial discharge capacity after the 150th cycle).

Fast screening method to characterize lithium ion battery electrolytes by means of solid phase microextraction – gas chromatography – mass spectrometry

Several electrolytes of commercially available lithium ion batteries (LIBs) were analyzed by solid phase microextraction – gas chromatography – mass spectrometry (SPME-GC-MS). The uptake and subsequent injection of the conducting salt LiPF6 into the GC system was prevented by using a headspace SPME setup. Thus, a removal step prior to the GC-MS measurements was not necessary and it was possible to analyze the untreated electrolyte without injecting the hazardous LiPF6 into the GC system. Furthermore, all SPME experiments were carried out at room temperature to exclude further thermal alteration of the electrolyte during sampling. In LIB electrolytes, different linear and cyclic carbonate solvents and additives such as succinonitrile (SN) and fluoroethylene carbonate (FEC) could be identified using the SPME-GC-MS setup. Moreover, the aging products dimethyl-2,5-dioxahexane dicarboxylate (DMDOHC) and ethylmethyl-2,5-dioxahexane dicarboxylate (EMDOHC) were identified in the electrolyte of aged 18 650-type cells. In the case of the cells of one specific supplier, various additional hydrocarbons were detected via SPME-GC-MS. These compounds could not be obtained when a GC-MS setup with conventional liquid or headspace injection is used. Consecutive experiments were carried out by extracting the electrolyte components directly from the headspace above anode, separator and cathode of an aged 18 650-type cell, which confirmed the findings of the prior analysis of pure electrolytes. Within this work it was possible to develop a method for the investigation of LIB electrolytes and their decomposition products with high sensitivity and low GC column bleeding.