Jonas Mindemark

Illuminating the electrolyte in light-emitting electrochemical cells

Light-emitting electrochemical cells (LECs) convert electric current to light within an active material comprising an electroluminescent organic semiconductor and an electrolyte. It is well established that it is the presence of this electrolyte that enabled the recent development of low-cost fabrication methods of functional LECs as well as the realisation of unique device architectures. At the same time, it should be acknowledged that the current lower performance of LECs in comparison to the more commonplace organic light-emitting diode, at least in part, is intimately linked to the utilisation of non-ideal electrolytes. In this review, we present the tasks that the electrolyte should fulfil during the various stages of LEC operation, and how the characteristics of the electrolyte can affect the LEC performance, specifically the turn-on time, the efficiency and the operational stability. We thereafter introduce the different classes of electrolytes that have been implemented in LEC devices up to date, and discuss how these electrolytes have been able to meet the specific requirements of the LEC technology.

At the polymer electrolyte interfaces: the role of the polymer host in interphase layer formation in Li-batteries

In this study, X-ray photoelectron spectroscopy was applied for compositional analysis of the interphase layers formed in graphite and LiFePO4 Li-battery half cells containing solid polymer electrolytes (SPEs) consisting of poly(trimethylene carbonate) (PTMC) and LiTFSI salt. Decomposition of PTMC was observed at the anode/SPE interface, indicating different reaction products than those associated with the more conventional host material poly(ethylene oxide). Degradation mechanisms of the PTMC host material at low potentials are proposed. Compared to the LiFePO4/PEO interface, the absence of LiOH - a result of water contamination - was generally seen when using hydrophobic PTMC as the polymer host. A clear correlation of moisture content with the constitution of interphase layers in Li polymer batteries could thus be concluded. At the SPE/LiFePO4 interface, good stability was seen regardless of the polymer host materials.

Ion transport in polycarbonate based solid polymer electrolytes: experimental and computational investigations

Among the alternative host materials for solid polymer electrolytes (SPEs), polycarbonates have recently shown promising functionality in all-solid-state lithium batteries from ambient to elevated temperatures. While the computational and experimental investigations of ion conduction in conventional polyethers have been extensive, the ion transport in polycarbonates has been much less studied. The present work investigates the ionic transport behavior in SPEs based on poly(trimethylene carbonate) (PTMC) and its co-polymer with ε-caprolactone (CL) via both experimental and computational approaches. FTIR spectra indicated a preferential local coordination between Li(+) and ester carbonyl oxygen atoms in the P(TMC20CL80) co-polymer SPE. Diffusion NMR revealed that the co-polymer SPE also displays higher ion mobilities than PTMC. For both systems, locally oriented polymer domains, a few hundred nanometers in size and with limited connections between them, were inferred from the NMR spin relaxation and diffusion data. Potentiostatic polarization experiments revealed notably higher cationic transference numbers in the polycarbonate based SPEs as compared to conventional polyether based SPEs. In addition, MD simulations provided atomic-scale insight into the structure-dynamics properties, including confirmation of a preferential Li(+)-carbonyl oxygen atom coordination, with a preference in coordination to the ester based monomers. A coupling of the Li-ion dynamics to the polymer chain dynamics was indicated by both simulations and experiments.

Diversity in cyclic carbonates: synthesis of triazole-functional monomers using click chemistry

Triazole-functional cyclic carbonates are presented as a new class of functional monomers for ring-opening polymerisation. Starting from bromo-functional six-membered cyclic carbonates, a series of triazole-functional monomers was synthesised using click chemistry. This synthetic strategy allows for facile synthesis of a great number of structurally diverse monomers from just a few azide-functional precursors.

Hydroxyl-functionalized poly(trimethylene carbonate) electrolytes for 3D-electrode configurations

Polymer electrolytes were prepared from an aliphatic polycarbonate with 10 mol% of repeating units having a hydroxyl-functional side group, with the addition of LiTFSI salt. The hydrogen bond-interacting side groups were found to be beneficial for improving adhesion to 2D planar electrode material surfaces. These favorable surface properties proved to be valid also for 3D-structured systems since thin, conformal coatings could be cast on 3D-microstructured electrodes. In addition, the electrolytes were found to have reasonable ionic conductivity (up to 2.7 × 10−8 S cm−1 at 25 °C and 2.3 × 10−6 S cm−1 at 60 °C) that was almost independent of salt concentration. This demonstrates how a hydroxyl-functional polymer approach is suitable for the creation of 3D-structured electrode–electrolyte assemblies for microbattery applications.

Low Charge Density Cationic Polymers for Gene Delivery: Exploring the Influence of Structural Elements on in vitro Transfection

A series of end-functionalized poly(trimethylene carbonate) DNA carriers, characterized by low cationic charge density and pronounced hydrophobicity, is used to study structural effects on in vitro gene delivery. As the DNA-binding moieties are identical in all polymer structures, the differences observed between the different polymers are directly related to the functionality and length of the polymer backbone. The transfection efficiency and cytotoxicity of the polymer/DNA complexes are thus found to be dependent on a combination of polymer charge density and functionality, highlighting the importance of such structural considerations in the development of materials for efficient gene delivery.

Efficient DNA binding and condensation using low molecular weight, low charge density cationic polymer amphiphiles.

A new class of biodegradable cationic macromolecules for DNA binding and condensation was developed by end-group-functionalization of poly(trimethylene carbonate). A series of one- and two-armed structures was synthesized and their interaction with DNA was evaluated. To aid data interpretation, a non-linear modeling method was applied to show efficient DNA binding that was intimately related to cationic charge density and macromolecular architecture. One-armed, low charge density structures were consistently found to bind to DNA at lower charge ratios than their two-armed, high charge density counterparts. This suggests that polymer backbone structure and characteristics are important considerations in the development of efficient cationic polymer systems for DNA condensation and delivery.

A new resorbable device for ligation of blood vessels - a pilot study.

BackgroundDuring surgery, controlled haemostasis to prevent blood loss is vital for a successful outcome. It can be difficult to ligate vessels located deep in the abdomen. A device that is easy to use and enables secure ligatures could be beneficial. Cable ties made of nylon have been used for ligation but the non-resorbable material caused tissue reactions. The objective of this study was to use a resorbable material to construct a device with a self-locking mechanism and to test its mechanical strength and ligation efficiency.MethodsThe device was manufactured by injection moulding of polydioxanone, a resorbable polymer used for suture materials. Polydioxanone with inherent viscosities of 1.9 dL/g and 1.3 dL/g were tested. The device consisted of a perforated flexible band which could be pulled through a case with a locking mechanism. After a first version of the device had been tested, some improvements were made. The locking case was downsized, corners were rounded off, the band was made thicker and the mould was redesigned to produce longer devices. Tensile tests were performed with the second version.The first version of the device was used to ligate the ovarian pedicle in a euthanized dog and to test echogenicity of the device with ultrasound. Compression of vessels of the ovarian pedicle was examined by histology. Both versions of the device were tested for haemostasis of and tissue grip on renal arteries in six anaesthetised pigs.ResultsThe tensile strength of the flexible band of the devices with inherent viscosity of 1.9 dL/g was 50.1 ± 5.5 N (range 35.2-62.9 N, n = 11) and the devices with inherent viscosity of 1.3 dL/g had a tensile strength of 39.8 ± 8.1 N (range 18.6-54.2 N, n = 11). Injection moulding of the polymer with lower inherent viscosity resulted in a longer flow distance.Both versions of the device had an effective tissue grip and complete haemostasis of renal arteries was verified. The device attached to the ovarian pedicle could be seen with ultrasound, and vessel compression and occlusion were verified by histology.ConclusionsTests of functionality of the device showed complete haemostasis and good tissue grip. Devices with a band of sufficient length were easily applied and tightened in tissue.

The Weak Microcavity as an Enabler for Bright and Fault-tolerant Light-emitting Electrochemical Cells

The light-emitting electrochemical cell (LEC) is functional at substantial active-layer thickness, and is as such heralded for being fit for low-cost and fault-tolerant solution-based fabrication. We report here that this statement should be moderated, and that in order to obtain a strong luminous output, it is fundamentally important to fabricate LEC devices with a designed thickness of the active layer. By systematic experimentation and simulation, we demonstrate that weak optical microcavity effects are prominent in a common LEC system, and that the luminance and efficiency, as well as the emission color and the angular intensity, vary in a periodic manner with the active-layer thickness. Importantly, we demonstrate that high-performance light-emission can be attained from LEC devices with a significant active-layer thickness of 300 nm, which implies that low-cost solution-processed LECs are indeed a realistic option, provided that the device structure has been appropriately designed from an optical perspective.

Toward Solid-State 3D-Microbatteries Using Functionalized Polycarbonate-Based Polymer Electrolytes

3D microbatteries (3D-MBs) impose new demands for the selection, fabrication, and compatibility of the different battery components. Herein, solid polymer electrolytes (SPEs) based on poly(trimethylene carbonate) (PTMC) have been implemented in 3D-MB systems. 3D electrodes of two different architectures, LiFePO4-coated carbon foams and Cu2O-coated Cu nanopillars, have been coated with SPEs and used in Li cells. Functionalized PTMC with hydroxyl end groups was found to enable uniform and well-covering coatings on LiFePO4-coated carbon foams, which was difficult to achieve for nonfunctionalized polymers, but the cell cycling performance was limited. By employing a SPE prepared from a copolymer of TMC and caprolactone (CL), with higher ionic conductivity, Li cells composed of Cu2O-coated Cu nanopillars were constructed and tested both at ambient temperature and 60 °C. The footprint areal capacity of the cells was ca. 0.02 mAh cm-2 for an area gain factor (AF) of 2.5, and 0.2 mAh cm-2 for a relatively dense nanopillar-array (AF = 25) at a current density of 0.008 mA cm-2 under ambient temperature (22 ± 1 °C). These results provide new routes toward the realization of all-solid-state 3D-MBs.