Emulsion polymerizations for a sustainable preparation of efficient TEMPO‐based electrodes

Organic polymer‐based batteries represent a promising alternative to present‐day metal‐based systems and a valuable step toward printable and customizable energy storage devices. However, most scientific work is focussed on the development of new redox‐active organic materials, while straightforward manufacturing and sustainable materials and production will be a necessary key for the transformation to mass market applications. Here, a new synthetic approach for 2,2,6,6‐tetramethyl‐4‐piperinidyl‐ N ‐oxyl (TEMPO)‐based polymer particles by emulsion polymerization and their electrochemical investigation are reported. The developed emulsion polymerization protocol based on an aqueous reaction medium allowed the sustainable synthesis of a redox‐active electrode material, combined with simple variation of the polymer particle size, which enabled the preparation of nanoparticles from 35 to 138 nm. Their application in cell experiments revealed a significant effect of the size of the active‐polymer particles on the performance of poly(2,2,6,6‐tetramethyl‐4‐piperinidyl‐ N ‐oxyl methacrylate) (PTMA)‐based electrodes. In particular rate capabilities were found to be reduced with larger diameters. Nevertheless, all cells based on the different particles revealed the ability to recover from temporary capacity loss due to application of very high charge/discharge rates.Sustainable and efficient organic electrode : A new synthetic approach for polymers for organic batteries includes an emulsion polymerization with adjustable particle sizes in aqueous dispersions and allows the sustainable manufacturing of active materials and composite electrodes. The electrochemical investigation shows that the influence of particle sizes and the resulting morphologies of composite films on the cell performance is as important as the active material itself

Boehmite-based ceramic separator for lithium-ion batteries

A free-standing ceramic separator for lithium-ion batteries based on synthesized and surface-functionalized boehmite nanoparticles (AlO(OH)) was prepared by means of a pilot coating machine. For this composite membrane, polyvinylidene difluoride (PVdF) homopolymer was used as a binder. The separator displays a homogeneous morphology with a thickness of 22 µm. The mean pore size of the separator is 64 nm and the MacMullin number is 5.1. The constant current cycling behavior and C-rate capability up to 5 C are comparable to those of a commercial tri-layer polyolefin separator. Even though the mechanical properties of the ceramic separator are in some regards comparable to those of the polyolefin separator, however, they need to be improved so that the ceramic separator is able to withstand the stressful cell assembly process. Moreover, the boehmite-based ceramic separator displays a superior wettability and thermal stability compared to state-of-the-art polyolefin separators and is, therefore very promising for application in lithium-ion batteries

Results from a Novel Method for Corrosion Studies of Electroplated Lithium Metal Based on Measurements with an Impedance Scanning Electrochemical Quartz Crystal Microbalance

A new approach to study the chemical stability of electrodeposited lithium on a copper metal substrate via measurements with a fast impedance scanning electrochemical quartz crystal microbalance is presented. The corrosion of electrochemically deposited lithium was compared in two different electrolytes, based on lithium difluoro(oxalato) borate (LiDFOB) and lithium hexafluorophosphate, both salts being dissolved in solvent blends of ethylene carbonate and diethyl carbonate. For a better understanding of the corrosion mechanisms, scanning electron microscopy images of electrodeposited lithium were also consulted. The results of the EQCM experiments were supported by AC impedance measurements and clearly showed two different corrosion mechanisms caused by the different salts and the formed SEIs. The observed mass decrease of the quartz sensor of the LiDFOB-based electrolyte is not smooth, but rather composed of a series of abrupt mass fluctuations in contrast to that of the lithium hexafluorophosphate-based electrolyte. After each slow decrease of mass a rather fast increase of mass is observed several times. The slow mass decrease can be attributed to a consolidation process of the SEI or to the partial dissolution of the SEI leaving finally lithium metal unprotected so that a fast film formation sets in entailing the observed fast mass increases

Adaptation of electrodes and printable gel polymer electrolytes for optimized fully organic batteries

Abstract Despite intensive scientific efforts on the development of organic batteries, their full potential is still not being realized. The individual components, such as electrode materials and electrolytes, are in most cases developed independently and are not adjusted to each other. In this context, we report on the performance optimization of a full‐organic solid‐state battery system by the mutual adaptation of the electrode materials and an ionic liquid (IL)‐based gel polymer electrolyte (GPE). The formulation of the latter was designed for a one‐step manufacturing approach and can be applied directly to the electrode surface, where it is UV‐cured to yield the GPE without further post‐treatment steps. Herein, a special focus was placed on the applicability in industrial processes. A first significant capacity increase was achieved by the incorporation of the IL into the electrode composite. Furthermore, the GPE composition was adapted applying acrylate‐ and methacrylate‐based monomers and combinations thereof with the premise of a fast curing step. Furthermore, the amount of IL was varied, and all combinations were evaluated for their final performance in cells. The latter variation revealed that a high ionic conductivity is not the only determining factor for a good cell performance. Next to a sufficient conductivity, the interaction between electrode and electrolyte plays a key role for the cell performance as it enhances the accessibility of the counter ions to the redox‐active sites

Methyl tetrafluoro-2-(methoxy) propionate as co-solvent for propylene carbonate-based electrolytes for lithium-ion batteries

Methyl tetrafluoro-2-(methoxy) propionate (MTFMP) was evaluated as co-solvent for PC-based electrolytes in combination with graphite electrodes. Already 10 wt% (5.6 mol%) of MTFMP in PC were sufficient to form an effective and stable SEI on graphite as confirmed by battery tests. In the first cycle, the formation of an effective SEI via the decomposition of MTFMP was observed before PC co-intercalation thus preventing the subsequent exfoliation of the graphite. The stability of this SEI was verified by long term cycling tests, which showed that the capacity loss of the graphite-based cell was only 1.3% after 300 cycles at 1 C. The electrolyte, 1 M LiPF 6 in PC:MTFMP (9:1 wt%), showed also a good rate capability up to 5 C on graphite. Therefore, MTFMP can be considered as a new, very promising co-solvent for PC-based electrolytes for use in lithium-ion batteries with graphite anodes. © 2012 Elsevier B.V. All rights reserved