Browsing by Author "Hemmerling, Jessica"

Now showing 1 - 5 of 5

Open Access
Comparison of different current collector materials for in situ lithium deposition with slurry-based solid electrolyte layers
(2023) Kreher, Tina; Heim, Fabian; Pross-Brakhage, Julia; Hemmerling, Jessica; Birke, Kai Peter
In this paper, we investigate different current collector materials for in situ deposition of lithium using a slurry-based β-Li3PS4 electrolyte layer with a focus on transferability to industrial production. Therefore, half-cells with different current collector materials (carbon-coated aluminum, stainless steel, aluminum, nickel) are prepared and plating/stripping tests are performed. The results are compared in terms of Coulombic efficiency (CE) and overvoltages. The stainless steel current collector shows the best performance, with a mean efficiency of ηmean,SST=98%; the carbon-coated aluminum reaches ηmean,Al+C=97%. The results for pure aluminum and nickel indicate strong side reactions. In addition, an approach is tested in which a solvate ionic liquid (SIL) is added to the solid electrolyte layer. Compared to the cell setup without SIL, this cannot further increase the CE; however, a significant reduction in overvoltages is achieved.
Open Access
High flashpoint and eco-friendly electrolyte solvent for lithium-ion batteries
(2023) Ströbel, Marco; Kiefer, Larissa; Pross-Brakhage, Julia; Hemmerling, Jessica; Finster, Philipp; Ziebert, Carlos; Birke, Kai Peter
Since Sony launched the commercial lithium-ion cell in 1991, the composition of the liquid electrolytes has changed only slightly. The electrolyte consists of highly flammable solvents and thus poses a safety risk. Solid-state ion conductors, classified as non-combustible and safe, are being researched worldwide. However, they still have a long way to go before being available for commercial cells. As an alternative, this study presents glyceryl tributyrate (GTB) as a flame retardant and eco-friendly solvent for liquid electrolytes for lithium-ion cells. The remarkably high flashpoint (𝑇FP=174∘C) and the boiling point (𝑇BP=287∘C) of GTB are approximately 150 K higher than that of conventional linear carbonate components, such as ethyl methyl carbonate (EMC) or diethyl carbonate (DEC). The melting point (𝑇MP=-75∘C) is more than 100 K lower than that of ethylene carbonate (EC). A life cycle test of graphite/NCM with 1 M LiTFSI dissolved in GTB:EC (85:15 wt) achieved a Coulombic efficiency of above 99.6% and the remaining capacity resulted in 97% after 50 cycles (𝐶/4) of testing. The flashpoint of the created electrolyte is 𝑇FP=172∘C and, therefore, more than 130 K higher than that of state-of-the-art liquid electrolytes. Furthermore, no thermal runaway was observed during thermal abuse tests. Compared to the reference electrolyte LP40, the conductivity of the GTB-based is reduced, but the electrochemical stability is highly improved. GTB-based electrolytes are considered an interesting alternative for improving the thermal stability and safety of lithium-ion cells, especially in low power-density applications.
Open Access
Non-uniform circumferential expansion of cylindrical Li-ion cells - the potato effect
(2021) Hemmerling, Jessica; Guhathakurta, Jajnabalkya; Dettinger, Falk; Fill, Alexander; Birke, Kai Peter
This paper presents the non-uniform change in cell thickness of cylindrical Lithium (Li)-ion cells due to the change of State of Charge (SoC). Using optical measurement methods, with the aid of a laser light band micrometer, the expansion and contraction are determined over a complete charge and discharge cycle. The cell is rotated around its own axis by an angle of α=10° in each step, so that the different positions can be compared with each other over the circumference. The experimental data show that, contrary to the assumption based on the physical properties of electrode growth due to lithium intercalation in the graphite, the cell does not expand uniformly. Depending on the position and orientation of the cell coil, there are different zones of expansion and contraction. In order to confirm the non-uniform expansion around the circumference of the cell in 3D, X-ray computed tomography (CT) scans of the cells are performed at low and at high SoC. Comparison of the high resolution 3D reconstructed volumes clearly visualizes a sinusoidal pattern for non-uniform expansion. From the 3D volume, it can be confirmed that the thickness variation does not vary significantly over the height of the battery cell due to the observed mechanisms. However, a slight decrease in the volume change towards the poles of the battery cells due to the higher stiffness can be monitored.
Open Access
Non-uniform circumferential expansion of cylindrical Li-ion cells : the potato effect
(2021) Hemmerling, Jessica; Guhathakurta, Jajnabalkya; Dettinger, Falk; Fill, Alexander; Birke, Kai Peter
This paper presents the non-uniform change in cell thickness of cylindrical Lithium (Li)-ion cells due to the change of State of Charge (SoC). Using optical measurement methods, with the aid of a laser light band micrometer, the expansion and contraction are determined over a complete charge and discharge cycle. The cell is rotated around its own axis by an angle of α=10° in each step, so that the different positions can be compared with each other over the circumference. The experimental data show that, contrary to the assumption based on the physical properties of electrode growth due to lithium intercalation in the graphite, the cell does not expand uniformly. Depending on the position and orientation of the cell coil, there are different zones of expansion and contraction. In order to confirm the non-uniform expansion around the circumference of the cell in 3D, X-ray computed tomography (CT) scans of the cells are performed at low and at high SoC. Comparison of the high resolution 3D reconstructed volumes clearly visualizes a sinusoidal pattern for non-uniform expansion. From the 3D volume, it can be confirmed that the thickness variation does not vary significantly over the height of the battery cell due to the observed mechanisms. However, a slight decrease in the volume change towards the poles of the battery cells due to the higher stiffness can be monitored.
Open Access
Untersuchung der Zellausdehnung und des Gasinnendrucks zylindrischer Lithium-Ionen Zellen
(2025) Hemmerling, Jessica; Birke, Kai Peter (Prof. Dr.-Ing)