Recent advances in poly(Vinylidene fluoride) and its copolymers for lithium-ion battery separators

The separator membrane is an essential component of lithium-ion batteries, separating the anode and cathode, and controlling the number and mobility of the lithium ions. Among the polymer matrices most commonly investigated for battery separators are poly(vinylidene fluoride) (PVDF) and its copolymers poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), and poly(vinylidene fluoride-cochlorotrifluoroethylene) (PVDF-CTFE), due to their excellent properties such as high polarity and the possibility of controlling the porosity of the materials through binary and ternary polymer/solvent systems, among others. This review presents the recent advances on battery separators based on PVDF and its copolymers for lithium-ion batteries. It is divided into the following sections: single polymer and co-polymers, surface modification, composites, and polymer blends. Further, a critical comparison between those membranes and other separator membranes is presented, as well as the future trends on this area.Portuguese Foundation for Science and Technology (FCT): UID/FIS/04650/2013, PTDC/CTM-ENE/5387/2014, UID/CTM/50025/2013, project NO. 28157/02/SAICT/2017 and grants SFRH/BPD/112547/2015 (C.M.C.), including FEDER funds through the COMPETE 2020 programme and National Funds through FCT. Financial support from the Basque Government Industry Department under the ELKARTEK and HAZITEK programs is also acknowledged.info:eu-repo/semantics/publishedVersio

Synthetic polymer-based membrane for lithium Ion batteries

Efficient energy storage systems are increasingly needed due to advances in portable electronics and transport vehicles, lithium-ion batteries standing out among the most suitable energy storage systems for a large variety of applications. In lithium-ion batteries, the porous separator membrane plays a relevant role as it is placed between the electrodes and serves as a charge transfer medium and affects the cycle behavior. Typically, porous separators membranes are comprised of a synthetic polymeric matrix embedded in the electrolyte solution. The present chapter focus on recent advances in synthetic polymers for porous separation membranes, as well as on the techniques for membrane preparation and physicochemical characterization. The main challenges to improve synthetic polymer performance for battery separator membrane applications are also discussed.Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2019, UID/QUI/50006/2019, UID/QUI/0686/2016 and UID/EMS/00151/2019. The authors thank FEDER funds through the COMPETE 2020 Programme and National Funds through FCT under the project PTDC/FIS-MAC/28157/2017, Grants 38 SFRH/BPD/117838/2016 (JNP). and SFRH/BPD/112547/2015 (C.M.C). Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) through the project MAT2016-76039-C4-3-R (AEI/FEDER, UE) (including the FEDER financial support) and from the Basque Government Industry and Education Departments under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06

Strategies to improve the electrochemical performance of lithium-ion batteries by stabilizing the interface of electrode/electrolyte

”Lithium-ion batteries (LIBs) provide great potential for electric vehicles, and smart grids as future energy-storage devices. However, there are many challenges in the development of the LIB industry, including low energy and power density of electrode materials, poor rate performance, short cycle life of electrode materials, and safety issues caused by the flammability of the conventional organic liquid electrolytes. In this research, we were committed to using general approach to efficiently and economically synthesize or modify LIB materials by stabilizing the interface between electrode and electrolyte. Atomic layer deposition (ALD) method was used to coat metal oxide thin films on commercial electrode materials, which assisted the electrodes to form a beneficial interface layer and protected the active materials from organic liquid electrolyte, improved the conductivity of the active material, and led to an improved electrochemical performance of the material. The problem of uneven distribution of polyvinylidene fluoride (PVDF) binder had been solved using an extremely simple heat treatment method, which led to a stable and inorganic-riched solid electrolyte interphase (SEI) layer that improved the specific capacities and capacity retentions of the anode electrodes. A low liquid leakage ceramic polymer electrolyte (CPE) with high porosity, thermal and electrochemical stability, and ionic conductivity was synthesized to solve the safety issue of the uncontrolled growth of lithium dendrites in the conventional LIBs. Ultra-thin ZrO2 films were coated on cathode particles by ALD to reduce the interfacial resistance for all-solid-state battery, which improved lithium ions transport and suppressed undesirable interfacial side reactions”--Abstract, page iv

The Processing and Characterization of Nano Composite Nano Fibers for Various Applications

The study of this thesis focuses on the force spinning of polymer composite nanofibers for antibacterial and energy storage applications. For energy application, Polyacrylonitrile (PAN), Polymethyl methacrylate (PMMA) polymers with active materials (Sn & Ti) and for antibacterial purposes, Polyvinylpyrrolidone (PVP) and Polyethylene-oxide (PEO) polymers along with NPs (Ag and Cu), both were centrifugally spun to get finer nanofibers. The spun produced nanofibers of each types ascertained the percentage of active materials accurately. Antibacterial test on PEO/Ag composite nanofibers exhibited 100% inhibition efficiency against E. coli and B. cereus bacteria while PVP/Cu, PEO/Cu fibrous membranes showed 97.98%, 98.99% respectively. CuNPs and AgNPswere well embedded onto nanofibers at nanoscale level, assisting to inhibit bacterial growth. On the other hand, as an energy storage anode material, force spun, and coated PAN/PMMA/SnO2/TiO2 composite nanofibers displayed excellent electrochemical performances in sodium ion battery (SIB). Volume expansion, capacity fading are regular problems of SnO2 anode, however SnO2 coupled with TiO2 facilitated stabilized capacity retention along with cycle stability. Centrifugally spun PAN/PMMA/SnO2/TiO2 nanofibers showed lower capacity fading and more stability than SnO2/TiO2 coated nanofibers. Additionally, carbonized PAN/PMMA nanofibers coated with SnO2/TiO2 anode performed better rate capacity and stability over prolonged cycles than slurry-based anode since coating assists to packing metal oxides short fibers-throughout intra and inter layers uniformly. Such an effective anode and strong antibacterial agent obtained from force spun composite fibers could be promising for energy and biomedical applications in future

Lithium-ion battery separator membranes based on poly(L-lactic acid) biopolymer

Sustainable materials are increasingly needed in lithium ion batteries in order to reduce their environmental impact and improve their recyclability. This work reports on the production of separators using poly (L-lactic acid) (PLLA) for lithium ion battery applications. PLLA separators were obtained by solvent casting technique, by varying polymer concentration in solution between 8 wt.% and 12 wt.% in order to evaluate their morphology, thermal, electrical and electrochemical properties. It is verified that morphology and porosity can be tuned by varying polymer concentration and that the separators are thermally stable up to 250 ºC. The best ionic conductivity of 1.6 mS/cm was obtained for the PLLA separator prepared from 10 wt.% polymer concentration in solution, due to the synergistic effect of the morphology and electrolyte uptake. For this membrane, a high discharge capacity value of 93 mAh.g-1 was obtained at the rate of 1C. In this work, it is demonstrated that PLLA is a good candidate for the development of separator membranes, in order to produce greener and environmentally friendly batteries in a circular economy context.Work supported by the Portuguese Foundation for Science and Technology (FCT) undes strategic funding UID/FIS/04650/2020 and UID/QUI/0686/2020, project PTDC/FISMAC/28157/2017, and Grants SFRH/BD/140842/2018 (J.C.B.), SFRH/BPD/121526/2016 (D.M.C), CEECIND/00833/2017 (R.G.) and SFRH/BPD/112547/2015 (C.M.C.). Financial support from the Basque Government Industry Department under the ELKARTEK and HAZITEK programs is also acknowledged. Technical and human support provided by SGIker (UPV/EHU, MICINN, GV/EJ, EGEF and ESF) is gratefully acknowledge

Electroactive polymer based porous membranes for energy storage applications

Tese de doutoramento em Ciências (ramo de conhecimento em Física)In the field of mobile applications the efficient storage of energy is one of the most critical issues. Lithium ion batteries are lighter, cheaper, show higher energy density (210Wh kg-1), no memory effect, longer service-life and higher number of charge/discharge cycles than other battery solutions. The separator membrane is placed between the anode and cathode and serves as the medium for the transfer of charge, being a critical components for the performance of the batteries. Polymers such as PVDF and its copolymers poly(vinylidene fluoride-co-trifluoroethylene), P(VDF-TrFE), poly(vinylidene fluoride-co-hexafluoropropylene), P(VDF-HFP), and poly(vinylidene fluoride-co-chlorotrifluoroethylene), P(VDF-CTFE) are increasingly investigated for their use as battery separators due to their high polarity, excellent thermal and mechanical properties, controllable porosity and wettability by organic solvents, being also chemically inert and stable in cathodic environment. Despite previous works in some of the PVDF co-polymers, there is no systematic investigations on poly(vinylidene fluoride-trifluoroethylene), P(VDF-TrFE), despite its large potential for this specific application. The objective of this work is thus establish the suitability of P(VDF-TrFE) for battery separators and to control of its structure, stability and ionic conductivity in order to increase performance of the material as battery separators. It is shown that solvent evaporation at room temperature allows the preparation of membranes with degrees of porosity from 70% to 80% leading to electrolyte solution uptakes from 250% up to 600%. The preparation of composites of P(VDF-TrFE) with lithium salts allows ionic conductivity values of the electrolytes of 2.3×10−6 S/cm at 120 °C. These composites show good overall electrochemical stability. A novel type of polymer blend based on poly(vinylidene fluoride-trifluoroethylene)/poly(ethylene oxide), P(VDF-TrFE)/PEO, was prepared and it was found that the microstructure, hydrophilicity and electrolyte uptake strongly depend on PEO content within the blend. For this blend, the best value of ionic conductivity at room temperature was 0.25 mS cm−1 for the 60/40 membrane. It was also verified that the ionic conductivity of the membrane is depend on the anion size of the salts present in the electrolyte solution, affecting also the electrolyte uptake value Batteries fabricated with the separators developed in this work within Li/LiFePO4 and Li/Sn-C cells revealed very good cycling performance even at high current rates and 100% of depth of discharge (DOD), approaching the results achieved in liquid electrolytes. Good rate capability was observed in Li/LiFePO4 cathode cells, being able to deliver at 2C more that 90% of the capacity discharged at 0.1C. These results, in conjunction with the approximately 100% coulombic efficiency, indicate very good electrolyte/electrode compatibility. Thus, the developed materials showed suitable thermal, mechanical and electrochemical characteristics as well as high performance in battery applications, indicating the possibility of fabricating lithium-ion batteries with the battery separators developed in this work.Na área dos dispositivos móveis, tais como telemóveis e computadores, o armazenamento eficiente de energia é um dos problemas críticos a resolver. As baterias de ião-lítio são mais leves, mais baratas, com maior densidade de energia (210Wh kg-1), sem efeito de memória, tempo de vida prolongado e maior número de ciclos de carga / descarga do que outras baterias, tais como as de níquel-cádmio. Um dos componentes essenciais para o desempenho das baterias é a membrana de separador, colocada entre o ánodo e o cátodo. Polímeros como o poli (fluoreto de vinilideno) (PVDF) e seus co-polímeros: poli (fluoreto de vinilideno-co-trifluoroetileno), P(VDF-TrFE), poli (fluoreto de vinilideno-co-hexafluoropropileno), P(VDF-HFP), e poli (fluoreto de vinilideno-co-clorotrifluoroetileno), P(VDF-CTFE) são investigados quanto à sua utilização como separador de bateria devido à sua elevada polaridade; excelentes propriedades mecânicas e térmicas; porosidade controlável; molhabilidade por solventes orgânicos; ser quimicamente inertes e estáveis em ambiente catódico. Existem trabalhos com alguns co-polímeros de PVDF, mas não há investigações sistemáticas sobre poli (fluoreto de vinilideno-trifluoroetileno), P(VDF-TrFE), apesar do seu grande potencial para esta aplicação específica. O objetivo deste trabalho é, determinar a performance do P(VDF-TrFE) para a sua utilização em separadores de baterias, controlando a sua estrutura, a estabilidade e a condutividade iónica, a fim de aumentar o desempenho do material. Mostra-se que a evaporação do solvente à temperatura ambiente permite a preparação das membranas com diferentes graus de porosidade desde 70% até 80%, e com absorção de electrólito entre 250% e 600%. A preparação de compósitos de P(VDF-TrFE) com sais de lítio permitiu obter uma condutividade iónica dos electrólitos de 2,3×10-6 S.cm-1 à 120ºC com boa estabilidade electroquímica. Um novo tipo de misturas de polímeros à base de poli (fluoreto de vinilideno - trifluoroetileno) / poli (óxido de etileno), P(VDF-TrFE)/PEO, foram preparadas tendo em conta que a microestrutura, hidrofilicidade e absorção de eletrólitos dependem fortemente do teor de PEO dentro da mistura. Para esta mistura, o melhor valor de condutividade iónica à temperatura ambiente foi de 0,25 mS.cm-1 para a membrana com composição 60/40. Verificou-se que a condutividade iónica da membrana depende do tamanho do anião do sal presente na solução de electrólito, afetando também o valor de absorção do electrólito. Baterias fabricadas com os separadores desenvolvidos neste trabalho foram avaliadas em células de Li/LiFePO4 e Li/Sn-C revelando muito bom desempenho cíclico, mesmo para taxas altas de varrimento e 100% de “depth of discharge”, DOD, aproximando-se dos resultados obtidos em eletrólitos líquidos. Igualmente, em células de cátodo Li/LiFePO4 foi obtido a 2C mais de 90% da capacidade descarregada à 0.1C. Estes resultados, em conjunto com a eficiência coulombica aproximadamente de 100%, indicam uma muito boa compatibilidade entre o electrólito e o eléctrodo. Assim, os materiais desenvolvidos neste trabalho apresentam características térmicas, mecânicas e eletroquímicas apropriadas para a fabricação de baterias de ião-lítio baseados nestes separadores.Fundação para a Ciência e a Tecnologia (FCT) grant SFRH/BD/68499/2010

Electrospun polymer nanofibers: the booming cutting edge technology

Electrospinning has been recognized as a simple and efficient technique for the fabrication of ultrathin fibers from a variety of materials including polymers, composite and ceramics. Significant progress has been made throughout the past years in electrospinning and the resulting fibrous structures have been exploited in a wide range of potential applications. This article reviews the state-of-art of electrospinning to prepare fibrous electrode materials and polymer electrolytes based on electrospun membranes in the view of their physical and electrochemical properties for the application in lithium batteries. The review covers the electrospinning process, the governing parameters and their influence on fiber or membrane morphology. After a brief discussion of some potential applications associated with the remarkable features of electrospun membranes, we highlight the exploitation of this cutting edge technology in lithium batteries. Finally the article is concluded with some personal perspectives on the future directions in the fascinating field of energy storag

Water-Soluble Polymers with Ceramic/Metal Nanoparticles for Use as Anode Materials in Lithium-Ion and Sodium-Ion Batteries

Aqueous solutions of poly(vinylpyrrolidone) (PVP) with 20, 25, and 28 wt.% concentrations were successfully spun into fibers by centrifugal spinning. The pristine PVP fibers were annealed and carbonized to produce flexible carbon fibers for use as binder-free anodes in lithium-ion and sodium-ion batteries. These flexible carbon fibers were prepared by developing a novel three-step heat treatment to reduce the residual stresses in the pristine PVP precursor fibers and to prevent fiber degradation during carbonization. The average diameters of the pristine, annealed, and carbonized fibers were obtained using scanning electron microscopy (SEM), which showed that the average diameter of the carbon fibers increased with increasing polymer concentration. Thermal characterization of the pristine and annealed fibers was carried out by thermogravimetric analysis (TGA). The TGA results showed that the annealed fibers yielded a residual mass percentage of 36.0 % while the pristine PVP fibers suffered a higher mass loss and only retained 26.5% of the original mass above 450 °C in an inert gas. The electrochemical performance of the carbon-fiber anodes was evaluated by conducting galvanostatic charge/discharge cycles, rate performance, cycle voltammetry experiments, and impedance tests. The 20, 25, and 28 wt.% derived binder-free anodes were tested in Li-ion and Na-ion half-cells. TiO2/C and Sn/C composite fibers were prepared by the centrifugal spinning of TiO2/PVP and Sn/PVP solutions and subsequent heat treatment. The successful preparation of centrifugally spun composite fibers from aqueous solutions was only achieved with TiO2. Based on existing results in the literature, a higher vapor pressure leads to faster solvent evaporation and promotes fiber formation. Thus, a mixture of 1:1 water:ethanol (wt./wt.) was used to prepare the Sn/PVP precursor fibers as well as TiO2/PVP precursor fibers. Nonetheless, the centrifugally spun Sn/C and TiO2/C composite fibers prepared with the PVP/water/ethanol precursor solutions had a larger average diameter than those prepared from PVP aqueous solutions, which affected their electrochemical performance. In order to understand the constraints impeding the formation of Sn/C composite fibers from aqueous solutions, the viscosity and surface tension of aqueous Sn/PVP and TiO2/PVP precursor solutions were investigated using a programable rheometer (BROOKFIELD, RVDV-III U) and Goniometer, Kyowa-DropMaster, respectively. The results showed that the addition of particles to the PVP aqueous solutions did not play a significant role in the viscosity nor the surface tension of the PVP aqueous solutions. Thus, other causes such as particle dispersion were investigated. It was observed that an inferior particle dispersion was obtained in water when compared to that in ethanol. Finally, alternative methods to produce composite fibers from polymer aqueous solutions are discussed for future research endeavors

Development of sodium hybrid quasi-solid electrolytes based on porous NASICON and ionic liquids

Lithium-ion batteries are currently the alternative of choice to overcome the increasing demand of energy. However, besides the scarcity of lithium and limited geolocation, it is believed that such batteries have already reached their maximum maturity. Sodium batteries emerge as an alternative to produce the new, so called, post-lithium batteries. In this study, we explore (i) the effect of sodium content and sintering temperature in solid electrolytes based in NASICON-type compounds and (ii) the use of two methodologies to obtain porous NASICON samples: application of natural substances and organic materials as pore-formers and freeze casting. The main purpose is the attainment of hybrid quasi-solid state electrolytes, with enhanced room temperature conductivity, based on porous ceramic electrolyte layers infiltrated with ionic liquids. Using this approach, porous samples with different microstructure and porous morphology and distribution were achieved, providing an enhancement in conductivity (ranging from 0.45 to 0.96 mS cm−1 at 30 °C) of one order of magnitude for infiltrated samples respect to pore-free samples. According to these results the porous NASICON might be considered as a functional macroporous inorganic separator that can act as a Na+ reservoir.The authors would like to thank the Agencia Española de Investigación /Fondo Europeo de Desarrollo Regional (FEDER/UE) for funding the projects PID2019-106662RBC43. This work has also been supported by Comunidad de Madrid (Spain) - multiannual agreement with UC3M ("Excelencia para el Profesorado Universitario" - EPUC3M04) - Fifth regional research plan 2016-2020