Crystallization studies and application of innovative solid polymer electrolytes for lithium batteries

206 p.En esta tesis de doctorado se estudiaron diferentes sistemas de electrolitos poliméricos, con el objetivo de ser utilizados en baterías de litio. Los sistemas poliméricos desarrolados se prepararon con la finalidad de mejorar las prestaciones de los electrolitos sílidos actuales en términos de conductividad iónica, numero de transferencia de litio, propiedades mecánicas a elevada temperatura o resistencia a la llama. El polióxido de etileno (PEO) es el polímero mas utilizado en la actualidad como electrolito de polímero sólido en baterías de litio, ya que presenta los valores mas altos de conductividad iónica, pero tiene algunos parametros mejorables como su estabilidad térmica, electroquímica y propiedades mecánicas. En esta tesis, se utilizó PEO y se estudió el efecto sobre la cristalinidad del PEO la adición de sal de litio (LiTFSI) y diferentes polímeros.Los sistemas de electrolitos estudiados en esta tesis fueron preparados como mezcla de polímero y utilizando copolímeros de bloque

Polyethylene Oxide/Sodium Sulfonamide Polymethacrylate Blends as Highly Conducting Single-Ion Solid Polymer Electrolytes

In this work, blends of polyethylene oxide (PEO) and poly(sodium 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethanesulfonyl) imide) (PNaMTFSI) in different compositions were investigated for their application as solid electrolytes for sodium batteries. PNaMTFSI and PEO are miscible, exhibiting only one Tg in the whole range of compositions. PNaMTFSI was shown to reduce the crystal growth rate of PEO crystals but increase PEO nucleation, making the overall crystallization rate higher in blends with 15 and 30 wt % PNaMTFSI. The ionic conductivity is also affected by the blend composition. The highest values of ionic conductivity were observed with 15 and 30 wt % PNaMTFSI at high temperatures equal to 5.84 × 10–5 and 7.74 × 10–5 S cm–1 at 85 °C, respectively, with values of sodium-ion transference numbers of higher than 0.83 and electrochemical stability between 3.5 and 4.5 V versus Na+/Na0 depending on the composition, which opens the possibility of its use in sodium batteries. Finally, a comparison was made between the effect of sodium and lithium on these types of electrolytes, showing that sodium electrolytes have a lower ionic conductivity due to the larger size of the Na cation. The differences in the spherulitic growth rate and overall crystallization rate between Li and Na-containing electrolytes were compared and rationalized in terms of the blends’ intermolecular interactions and the relative contribution of primary nucleation and growth.We acknowledge the funding by Agencia Estatal de Investigación (no. PLEC2021-007929). This work has received funding from the Basque Government through grant no. IT1503-22

Effect of Chemical Structure and Salt Concentration on the Crystallization and Ionic Conductivity of Aliphatic Polyethers

Poly(ethylene oxide) (PEO) is the most widely used polymer in the field of solid polymer electrolytes for batteries. It is well known that the crystallinity of polymer electrolytes strongly affects the ionic conductivity and its electrochemical performance. Nowadays, alternatives to PEO are actively researched in the battery community, showing higher ionic conductivity, electrochemical window, or working temperature range. In this work, we investigated polymer electrolytes based on aliphatic polyethers with a number of methylene units ranging from 2 to 12. Thus, the effect of the lithium bis(trifluoromethanesulfone) imide (LiTFSI) concentration on the crystallization behavior of the new aliphatic polyethers and their ionic conductivity was investigated. In all the cases, the degree of crystallinity and the overall crystallization rate of the polymers decreased drastically with 30 wt % LiTFSI addition. The salt acted as a low molecular diluent to the polyethers according to the expectation of the Flory-Huggins theory for polymer-diluent mixtures. By fitting our results to this theory, the value of the interaction energy density (B) between the polyether and the LiTFSI was calculated, and we show that the value of B must be small to obtain high ionic conductivity electrolytes.We wish to thank the National Council of Science and Technology (CONACYT), Mexico for the grant awarded to Jorge L. Olmedo Martinez (471837). We are grateful to the financial support of the European Commission through the project SUSPOL-EJD 642671 and European Research Council by Starting Grant Innovative Polymers for Energy Storage (iPes) 306250. Alejandro J. Muller acknowledges the support of MINECO through grant MAT2017-83014-C2-1-P. Leire Meabe thanks Spanish Ministry of Education, Culture and Sport for the predoctoral FPU

Competition between nucleation and confinement in the crystallization of poly(ethylene glycol)/ large aspect ratio hectorite nanocomposites

Unformatted preprint version of the submitted articleThe overall crystallization kinetics of polymer nanocomposites is determined by nucleation and crystal growth, which are both greatly affected by confinement. Heterogeneous nucleation is influenced by the interphase area between filler and polymer matrix. Starting with a homogeneous nematic aqueous dispersion of a mixture containing polyethylene glycol (PEG) and varying amounts of a high aspect ratio layered silicate (hectorite, Hec), nanocomposite films were casted displaying a systematic variation of the degree of PEG confinement. This is achieved by a partial phase segregation upon drying, where independently of filler content a thermodynamically stable, 1 dimensional crystalline hybrid with constant volume of intercalated PEG (0.81 nm corresponding to a fraction 75 wt% and 55 vol%, respectively) is formed. This intercalated hybrid phase is incorporated into segregated PEG domains. The segregation is a kinetically controlled process and the length scale of segregation increases with PEG available in surplus of the hybrid. Due to the very large lateral extension of the Hec, the segregated domains are increasingly two dimensional. As evidenced by transmission electron micrographs and powder X-ray diffraction, the segregation produces composite structures where, in dependency of filler content, PEG slabs of different thickness are separated by domains of the intercalated hybrid material. The crystallization behavior of these bi-phasic materials was investigated by Differential Scanning Calorimetry (DSC) and Polarized Light Optical Microscopy (PLOM). DSC results reveal a competition between the nucleating effect of Hec, which was particularly important at low amounts, and the PEG confinement effect at higher filler loadings. Applying a self-nucleation protocol, the nucleation efficiency of the hectorite was shown to be up to 67%. The isothermal crystallization kinetics accelerated at low Hec contents (nucleation), went through a maximum and then decreased (confinement) as Hec content increased. Additionaly, a clear correlation between filler content and the Avrami index was obtained supporting the increase in confinement as filler loading increased.The authors thank Florian Puchtler for producing the synthetic sodium hectorite, Marco Schwarzmann for the SEM and TEM measurements and sample preparation via cryo ion slicing, and Dr. Sabine Rosenfeldt for the SAXS measurements. We appreciate the support of the Keylab for Optical and Electron Microscopy and the Keylab for Small Scale Polymer Processing of the Bavarian Polymer Institute (BPI). This work was supported by the German Science Foundation (DFG) within the collaborative research project SFB 1357. J.M. acknowledges support from the Provincial Council of Gipuzkoa under the program Fellow Gipuzkoa and partial financial support to the IBERDROLA Foundation. J.L.O.M. wish to thank the National Council of Science and Technology (CONACYT) in México for his grant 471837. We acknowledge funding by Mineco MAT2017-83014-C2-1-P project and by the Basque Government through grant IT1309-19. This work has also received funding from the European Union´s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 778092

Lithium Borate Ionic Liquids as Single-Component Electrolytes for Batteries

Current electrolytes for lithium batteries are usually composed of at least two chemical compounds, an organic solvent such as a cyclic carbonate and a lithium salt such as LiPF6. Here, the concept of using a single-component electrolyte is demonstrated in lithium batteries based on new lithium borate ionic liquids at room temperature. The design concept of this class of lithium ionic liquids (LiILs) is based on an asymmetrically substituted central tetracoordinate boron atom with oligoethylene glycol groups, fluorinated electron-attracting groups, and one alkane group. The optimized borateLi+ LiILs show a high ionic conductivity value of >10−4 S cm−1 at 25 °C, high lithium transference numbers ( = 0.4 – 0.5) and electrochemical stability (>4 V). Some of the LiILs present high compatibility with lithium-metal electrodes showing stable polarization profiles in platting/stripping tests. The selected LiIL is investigated as single-component electrolytes in lithium-metal battery cells showing discharge capacity values in Li0/LiIL/lithium–iron phosphate and Li0/LiIL/lithium titanate cells of 124 and 75 mAh g−1, respectively, at a C-rate of 0.2 C and 65 °C with low-capacity loss.This work was funded and supported by a Grant for Basque Government through grant IT1309-19, and European Commission's funded Marie Skłodowska–Curie project POLYTE-EID (Project No. 765828) and Spanish MCIN/AEI/PID2020-119026GB-I00. G.G.-G. is grateful to “Secretaría de Educación, Ciencia, Tecnología e Innovación” from Ciudad de México for the postdoctoral fellowship through grant SECTEI/133/2019. G.G.-G. also thanks the PhD. IOSM for being the driving force and constant support

Multifunctional Ionic Polymers from Deep Eutectic Monomers Based on Polyphenols

Herein we report a novel family of deep eutectic monomers and the corresponding polymers, made of (meth)acrylic ammonium salts and a series of biobased polyphenols bearing catechol or pyrogallol motifs. Phenolic chemistry allows modulating molecular interactions by tuning the ionic polymer properties from soft adhesive to tough materials. For instance, pyrogallol and hydrocaffeic acid-derived ionic polymers showed outstanding adhesiveness (>1 MPa), while tannic acid/gallic acid polymers with dense hydrogen bond distribution afforded ultratough elastomers (stretchability ≈1000% and strength ≈3 MPa). Additionally, phenolic polymeric deep eutectic solvents (polyDES) featured metal complexation ability, antibacterial properties, and fast processability by digital light 3D printing.This work was supported by Marie Sklodowska-Curie Research and Innovation Staff Exchanges (RISE) under grant agreement no. 823989 “IONBIKE”. The financial support from CONICET and ANPCyT (PICT 2018-01032) (Argentina) is also gratefully acknowledged

Tuning the properties of a UV-polymerized, cross-linked solid polymer electrolyte for lithium batteries

Lithium metal anodes have been pursued for decades as a way to significantly increase the energy density of lithium-ion batteries. However, safety risks caused by flammable liquid electrolytes and short circuits due to lithium dendrite formation during cell cycling have so far prevented the use of lithium metal in commercial batteries. Solid polymer electrolytes (SPEs) offer a potential solution if their mechanical properties and ionic conductivity can be simultaneously engineered. Here, we introduce a family of SPEs that are scalable and easy to prepare with a photopolymerization process, synthesized from amphiphilic acrylic polymer conetworks based on poly(ethylene glycol), 2-hydroxy-ethylacrylate, norbornyl acrylate, and either lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) or a single-ion polymethacrylate as lithium-ion source. Several conetworks were synthesized and cycled, and their ionic conductivity, mechanical properties, and lithium transference number were characterized. A single-ion-conducting polymer electrolyte shows the best compromise between the different properties and extends the calendar life of the cell

Polyether Single and Double Crystalline Blends and the Effect of Lithium Salt on Their Crystallinity and Ionic Conductivity

In this work, blends of Poly(ethylene oxide), PEO, and poly(1,6-hexanediol), PHD, were prepared in a wide composition range. They were examined by Differential Scanning Calorimetry (DSC), Polarized Light Optical Microscopy (PLOM) and Wide Angle X-ray Scattering (WAXS). Based on the results obtained, the blends were partially miscible in the melt and their crystallization was a function of miscibility and composition. Crystallization triggered phase separation. In blends with higher PEO contents both phases were able to crystallize due to the limited miscibility in this composition range. On the other hand, the blends with higher PHD contents display higher miscibility and therefore, only the PHD phase could crystallize in them. A nucleation effect of the PHD phase on the PEO phase was detected, probably caused by a transference of impurities mechanism. Since PEO is widely used as electrolyte in lithium batteries, the PEO/PHD blends were studied with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI), and the effect of Li-salt concentration was studied. We found that the lithium salt preferentially dissolves in the PEO phase without significantly affecting the PHD component. While the Li-salt reduced the spherulite growth rate of the PEO phase within the blends, the overall crystallization rate was enhanced because of the strong nucleating effect of the PHD component. The ionic conductivity was also determined for the blends with Li-salt. At high temperatures (>70 °C), the conductivity is in the order of ~10−3 S cm−1, and as the temperature decreases, the crystallization of PHD was detected. This improved the self-standing character of the blend films at high temperatures as compared to the one of neat PEO.This work has received funding from Basque Government through grant IT1309-19

Influence of anion structure on thermal, mechanical and CO2 solubility properties of uv-cross-linked poly(Ethylene glycol) diacrylate iongels

PTDC/CTM-POL/2676/2014 UID/QUI/50006/2019 grant 471837 SFRH/BD/136963/2018 IF/00505/2014Iongel-based CO2 separation membranes were prepared by fast (< 1 min) UV-initiated polymerization of poly(ethylene glycol) diacrylate (PEGDA) in the presence of different ionic liquids (ILs) with the [C2mim]+ cation and anions such as [TFSI]−, [FSI]−, [C(CN)3]− and [B(CN)4]−. The four ILs were completely miscible with the non-ionic PEGDA network. Transparent and freestanding iongels containing between 60 and 90 %wt of IL were obtained and characterized by diverse techniques (FTIR, TGA, DSC, DMTA, SEM, CO2 solubility and pure gas permeability). The thermal and mechanical stability of the iongels, as well as CO2 solubility, were found to be strictly dependent on the IL content and the anion’s nature. The TGA results indicated that the iongels mostly follow the thermal profile of the respective neat ILs. The DMTA analysis revealed that the iongels based on fluorinated anions have higher storage modulus than those of cyano-functionalized anions. Conversely, the PEGDA–C(CN)3 iongels presented the highest CO2 solubility values ranging from 72 to 80 mmol/g. Single CO2 permeabilities of 583 ± 29 Barrer and ideal CO2/N2 selectivities of 66 ± 3 were obtained with the PEGDA–70 C(CN)3 iongel membrane. This work demonstrates that the combination of PEGDA with high contents of the best performing ILs is a promising and simple strategy, opening up new possibilities in the design of high-performance iongel membranes for CO2 separation.publishersversionpublishe