Logotyp: till Uppsala universitets webbplats

This work comprises the synthesis and characterization of a novel solid polymer electrolyte based on oligomeric polyetheramine substituted with a methacrylic group at one of its three chain ends. This modification introduces a bifunctionality to the PEA monomer it can act both as polymerizable unit and surfactant. Thin and pinhole-free polymer electrolyte layers could be constructed with thicknesses in the order of <1 mu m using UV-initiated polymerization. The electrolyte exhibits good electrochemical and chemical stability up to 4 V vs. Li+/Li. LiFePO4 cathode coated with the electrolyte was cycled against lithium at 60 degrees C, and displayed reasonable capacity values (similar to 140 mAh g(-1)) for 10 cycles, where after Li dendrite formation contributed to battery instabilities. 

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 x 10(-8) S cm(-1) at 25 degrees C and 2.3 x 10(-6) S cm(-1) at 60 degrees 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.

This paper reports the synthesis and application of high-molecular-weight poly(trimethylene carbonate) (PTMC) as a new host material for solid polymer electrolyte-based Li-ion batteries. PTMC was synthesized through bulk ring-opening polymerization of the cyclic monomer to yield a high-molecular-weight polymer to serve as a base material for the electrolytes. The thermal properties and ionic conductivity of polymer electrolytes with different salt ratios were measured by TGA/DSC and electrochemical impedance spectroscopy, respectively. The most conductive systems were found at [Li⁺]:[carbonate] ratios of 1:13 and 1:8, which showed electrochemical stability up to 5.0 V vs. Li/Li⁺ and an ionic conductivity on the order of 10^− 7 Scm(-1) at 60 °C. LiFePO₄ half-cells using the electrolytes demonstrated a plateau in the specific discharge capacity around 153 mAhg(-1) after long-term cycling. The functionality of the electrolytes for three-dimensional microbatteries was also confirmed.

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 epsilon-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.

The first characterization studies of the interface layer formed between a Li-ion battery electrode and a solid polymer electrolyte (SPE) are presented here. SPEs are well known for their electrochemical stability and excellent safety, and thus considered good alternatives to conventional liquid/gel electrolytes in high-energy density battery devices. This work comprises studies of solid electrolyte interphase (SEI) formation in SPE-based graphite|Li cells using X-ray photoelectron spectroscopy (XPS). SPEs based on high molecular weight poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt are studied. Large amounts of LiOH are observed, and the XPS results indicate a correlation with moisture contamination in the SPEs. The water contents are quantitatively determined to be in the range of hundreds of ppm in the pure PEO as well as in the polymer electrolytes, which are prepared by a conventional SPE preparation method using different batches of PEO and at different drying temperatures. Moreover, severe salt degradation is observed at the graphite-SPE interface after the 1st discharge, while the salt is found to be more stable at the Li-SPE interface or when using LiTFSI-based liquid electrolyte equivalents.