Microcapsule-based techniques for improving the safety of lithium-ion batteries

Lithium-ion batteries are vital energy storage devices due to their high specific energy density, lack of memory effect, and long cycle life. While they are predominantly used in small consumer electronics, new strategies for improving battery safety and lifetime are critical to the successful implementation of high-capacity, fast-charging materials required for advanced Li-ion battery applications. Currently, the presence of a volatile, combustible electrolyte and an oxidizing agent (Lithium oxide cathodes) make the Li-ion cell susceptible to fire and explosions. Thermal overheating, electrical overcharging, or mechanical damage can trigger thermal runaway, and if left unchecked, combustion of battery materials. To improve battery safety, autonomic, thermally-induced shutdown of Li-ion batteries is demonstrated by depositing thermoresponsive polymer microspheres onto battery anodes. When the internal temperature of the cell reaches a critical value, the microspheres melt and conformally coat the anode and/or separator with an ion insulating barrier, halting Li-ion transport and shutting down the cell permanently. Charge and discharge capacity is measured for Li-ion coin cells containing microsphere-coated anodes or separators as a function of capsule coverage. Scanning electron microscopy images of electrode surfaces from cells that have undergone autonomic shutdown provides evidence of melting, wetting, and re-solidification of polyethylene (PE) into the anode and polymer film formation at the anode/separator interface.As an extension of this autonomic shutdown approach, a particle-based separator capable of performing autonomic shutdown, but which reduces the shorting hazard posed by current bi- and tri-polymer commercial separators, is presented. This dual-particle separator is composed of hollow glass microspheres acting as a physical spacer between electrodes, and PE microspheres to impart autonomic shutdown functionality. An oil immersion technique is developed to simulate an overheating condition while the cell is cycling. Experimental protocols are developed to assess the performance of the separator in terms of its ability to perform autonomic shutdown and examine tested battery materials using scanning electron microscopy. Another approach to improving battery functionality is via the microencapsulation of battery additives. Currently, additives are added directly into a battery electrolyte, and while they typically perform their function given a sufficient loading, these additives often do so at the expense of battery performance. Microencapsulation allows for a high loading of additives to be incorporated into the cell and their release triggered only when and where they are needed. In this work, microencapsulation techniques are developed to successfully encapsulate 3-hexylthiophene, a stabilizing agent for high-voltage cathodes in Li-ion batteries and conductive polymer precursor, as well as the flame retardant Tris(2-choloroethyl phosphate) (TCP). Microcapsules containing 3-hexylthiophene are coated onto model battery electrodes and immersed in electrolyte. The microcapsule shell wall insulates the 3-hexylthiophene until the microcapsules are mechanically crushed and electropolymerization of the released core to form poly(3-ht) occurs under cyclic voltammetry. In addition, TCP was encapsulated using in situ polymerization. TCP-containing microcapsules are stable in electrolyte at room temperature, but are thermally triggered to release their payload at elevated temperatures. Experimental protocols are developed to study the in situ triggering and release of microencapsulated additives

Characterization Of Halogen-Free Core Material With Various Flame Retardants

The effect of three different types of halogen-free flame retardants, which are the intumescent ammonium polyphosphates (APP), melamine cyanurate (MC) and calcium borate (CaB) on epoxy/glass fiber composites was studied. The single and hybrid flame retardant fillers were used to investigate the composites fire properties, mechanical and thermal properties. In general, after decompose at 700oC, CaB leaves behind the highest residual content, which mainly comprises of chars and glassy substrates. This is followed by APP which decomposes and forms the chars, while MC decomposes mainly into volatile gases. Among the three types, APP performed the best in flame retardancy while CaB is not effective in this composite

Characterization Of Halogen-Free Core Material With Various Retardants

The effect of three different types of halogen-free flame retardants, which are the intumescent ammonium polyphosphates (APP), melamine cyanurate (MC) and calcium borate (CaB) on epoxy/glass fiber composites was studied. The single and hybrid flame retardant fillers were used to investigate the composites fire properties, mechanical and thermal properties. In general, after decompose at 700oC, CaB leaves behind the highest residual content, which mainly comprises of chars and glassy substrates. This is followed by APP which decomposes and forms the chars, while MC decomposes mainly into volatile gases. Among the three types, APP performed the best in flame retardancy while CaB is not effective in this composite. As for the mechanical properties of the composites, CaB gives the highest flexural strength while MC provides the highest flexural modulus to the composites. In terms of thermal properties, the flame retardants have lowered the thermal stability of the composites but did not significantly affect the coefficient of thermal expansion (CTE) and glass transition temperature (Tg). The second phase which studied on the hybrid system, found that APP-MC and APP-CaB according to 80-20 ratio gave synergistic effect on the fire properties to the composites. The hybrid compounds remain at V-O with improved LO1 reading. These hybrid's composition also gave Vhigher flexural strength, but was found not to affect the Tg and CTE. On the addition of 0.5 vol. % metal chelates into hybrid-flame retardant system, the fire resistance did not show any improvement in terms of their LOI values. The residual content of the flame retardants after decomposition have also decreased. The flexural properties, Tg and CTE were also not affected by the metal chelates

Characterization Of Halogen-Free Core Material With Various Flame Retardants

The effect of three different types of halogen-free flame retardants, which are the intumescent ammonium polyphosphates (APP), melamine cyanurate (MC) and calcium borate (CaB) on epoxy/glass fiber composites was studied. The single andhybrid flame retardant fillers were used to investigate the composites fire properties, mechanical and thermal properties. In general, after decompose at 700oC, CaB leaves behind the highest residual content, which mainly comprises of chars and glassy substrates. This is followed by APP which decomposes and forms the chars, while MC decomposes mainly into volatile gases. Among the three types, APP performed the best in flame retardancy while CaB is not effective in this composite. As for the mechanical properties of the composites, CaB gives the highest flexural strength while MC provides the highest flexural modulus to the composites. In terms of thermal properties, the flame retardants have lowered the thermal stability of the composites but did not significantly affect the coefficient of thermal expansion (CTE) and glass transition temperature (Tg). The second phase which studied on the hybrid system, found that APP-MC and APP-CaB according to 80-20 ratio gave synergistic effect on the fire properties to the composites. The hybrid compounds remain at Vhigher flexural strength, but was found not to affect the Tg and CTE. On the addition of 0.5 vol. % metal chelates into hybrid-flame retardant system, the fire resistance did not show any improvement in terms of their LOI values. The residual content of the flame retardants after decomposition have also decreased. The flexural properties, Tg and CTE were also not affected by the metal chelate

Surface modifications of natural fibers and synthesis of inorganic nanoparticles for tailoring of the interphase and the flame retardancy of green composites

This thesis wants to show some applications which exploit sol-gel methodologies and its advantages to solve industrial and technological problems inherent the use of polymer based bio-composites. These composites can show severe limitations due to the easy flammability of the polymer matrix; this behavior can significantly restrict the application fields of these materials, especially when the possibility of the use of the composites is strictly related to specific regulatory fire tests that have to be passed, hence ensuring public safety (e.g., in the aerospace industry). Additional limitations descend from the mechanical properties of the above mentioned bio-composites, which may be due to a low interfacial adhesion between the filler (e.g., natural fibers) and the polymer matrix. Sol-gel methodologies can improve the fire behavior and the mechanical properties of bio-composites through the in-situ synthesis of ceramic domains in the polymer network and the tailoring of the interphase between filler and matrix

Bio-based flame retardant for sustainable building materials

As new promising alternatives, novel bio-based materials are already developed to apply in construction sectors due to biodegradability, low toxicity, sustainability, renewability, and acceptable general properties. However, their flammability and need to guarantee a low fire risk in the constructions is also an essential factor to restrict their further application. This thesis focused on investigation of bio-based material with good flame-retardant performance and corresponding flame-retardant mechanism. The detailed investigation was developed by following stages: synthesis of bio-based flame retardant and its application in PLA; effect of bio-based flame retardant on the fire resistance and other properties of natural fiber reinforced PLA. Finally, the smouldering and combustion performances of the bio-based thermal insulation material made from natural fiber were studied as well. 1) On basis of bio-based concept, PA and THAM were selected as raw material to synthesize a novel flame retardant and the chemical structure was confirmed via some characterizations. Afterwards, this synthetic product PA-THAM was employed as an efficient flame retardant to PLA by melt mixing. This binary system showed an improvement in flame retardancy, which was achieved by a combination of heat transfer effect, slight dilution and barrier action. For example, only 3 wt% loading of PA-THAM imparted PLA-based biocomposite LOI value of 25.8% and UL 94 V-0 level, as well as a significant self-extinguishing ability was observed. Besides, the molten viscosity of biocomposite also demonstrated more reduction compared with neat PLA due to the lubrication of PA-THAM, while there was little change in the mechanical properties. 2) PA-THAM and corn pith cellulose (OCC) were combined via in-situ modification and used to prepare a PLA-based biocomposite. After OCC was modified by PA-THAM successfully, which was proved by SEM/ EDS, FTIR, and TGA, the effect of PA-THAM on thermal stability and fire behaviors of PLA-based composite were also investigated accordingly. 5 phr addition of PA-THAM enabled this natural fiber reinforced polymer biocomposite (NPC) to illustrate a 50 °C higher temperature at maximum degradation rate than control sample without additive, and an improvement was also obtained in flame retardant properties with an increase of LOI value, a reduction of PHRR, and more char residue. The predominant flame-retardant mechanism focused on the synergistic effect of PA-THAM and OCC that occurred in condensed phase. Besides, the same level introduction of PA-THAM improved the interfacial affinity between PLA and OCC that maintained good mechanical properties as well. 3) A bio-based thermal insulation material was made from corn pith cellulose, alginate, and bio-efficient flame retardants. After introducing these bio-based additives, the smouldering and flaming combustion behaviors were improved significantly. Compared with the reference sample, thermal insulation particleboard with 8 wt% loading of a mixture of PA-THAM and a sodium borate salt (DOT) increased the initial temperature of smoldering ignition by 70 ºC, and meanwhile, the value of PHRR in flaming combustion decreased by 25.5%. Furthermore, the thermal conductivity was hardly affected, while the temperature at which the maximum thermal degradation occured increased. The correlative flame retardant mechanism was attributed to a synergistic effect from both flame retardants, which promoted a formation of more stable charring layer at initial stage.Los materiales de base biológica ofrecen una alternativa prometedora para aplicaciones en el sector de la construcción, debido a que se trata de materiales biodegradables, renovables y de baja toxicidad. Sin embargo, su capacidad de inflamar y la necesidad de mantener un bajo riesgo frente a incendios en los edificios es un factor esencial para restringir su posterior aplicación. Esta tesis se ha centrado en el desarrollo de materiales de base biológica con buen comportamiento frente al fuego y la investigación de los mecanismos de los retardantes de llama involucrados. La investigación se desarrolló en tres etapas que se detallan a continuación. 1) Partiendo del concepto de base biológica, se seleccionaron PA y THAM como materias primas para sintetizar un nuevo retardante de llama y la estructura química se confirmó mediante la caracterización del compuesto resultante. Posteriormente, este producto sintético PA-THAM se empleó como un retardante de llama eficiente para PLA mediante mezcla fundida. Este sistema binario mostró una mejora en la resistencia al fuego, que se logró mediante una combinación de los efectos de transferencia de calor, ligera dilución y acción barrera. Por ejemplo, con sólo un 3% en peso de carga de PA-THAM se logró un valor de LOI de 25,8% del compuesto de PLA y un nivel UL 94 V-0, así como una capacidad de autoextinción significativa. Además, la viscosidad fundida del biocompuesto también se redujo en relación a la del PLA puro debido a la lubricación ejercida por el PA-THAM. Por otro lado, la adición del retardante ocasionó pocos cambios en las propiedades mecánicas. 2) El retardante basado en PA-THAM y la fracción fina obtenida triturando la médula de maíz (OCC) se combinaron mediante modificación in situ y se usaron para preparar un biocompuesto basado en PLA. La médula de maíz fue modificada con éxito con el PA-THAM, la cual cosa se demostró por SEM / EDS, FTIR y TGA, el efecto de PA-THAM sobre la estabilidad térmica y el comportamiento al fuego del material compuesto a base de PLA también fueron investigados. La adición de 5 phr de PA-THAM permitió a este biocompuesto reforzado con fibras naturales (NPC) alcanzar una temperatura 50 °C más alta en el punto de degradación máximo comparado con la muestra de control sin aditivo. También se obtuvo una mejora en el comportamiento al fuego con un aumento del valor de LOI, una reducción del pico máximo del ritmo de liberación de calor (PHRR), y una mayor formación de residuo carbonizado. El mecanismo ignífugo predominante se centró en el efecto sinérgico del PA-THAM y la OCC que ocurrió en la fase condensada. Además, el mismo nivel de introducción de PA-THAM mejoró la afinidad interfacial entre PLA y OCC que también mantuvo buenas propiedades mecánicas. 3) Se prepararon muestras de un material de aislamiento térmico de base biológica a partir de médula de maíz, alginato y retardantes de llama de origen biológico. La adición del retardante de llama de base biológica logró mejorar significativamente el comportamiento al fuego, y el fenómeno de combustión sin llama (smouldering). En comparación con la muestra de referencia, el panel aislante con una carga de 8% en peso de una mezcla de PA-THAM y una sal de borato de sodio (DOT) aumentó la temperatura inicial a la que se produce la combustión sin llama en 70 ºC y, permitió reducir el valor de PHRR en un 25.5%. Además, la conductividad térmica apenas se vio afectada, mientras que la temperatura a la que se produce el valor máximo de degradación térmica aumentó notablemente. El análisis del mecanismo de acción de los retardantes reveló la existencia de un efecto sinérgico de ambos retardantes de llama, que promovió la formación de una capa de carbonización más estable en la etapa inicial

Bio-based flame retardant for sustainable building materials

As new promising alternatives, novel bio-based materials are already developed to apply in construction sectors due to biodegradability, low toxicity, sustainability, renewability, and acceptable general properties. However, their flammability and need to guarantee a low fire risk in the constructions is also an essential factor to restrict their further application. This thesis focused on investigation of bio-based material with good flame-retardant performance and corresponding flame-retardant mechanism. The detailed investigation was developed by following stages: synthesis of bio-based flame retardant and its application in PLA; effect of bio-based flame retardant on the fire resistance and other properties of natural fiber reinforced PLA. Finally, the smouldering and combustion performances of the bio-based thermal insulation material made from natural fiber were studied as well. 1) On basis of bio-based concept, PA and THAM were selected as raw material to synthesize a novel flame retardant and the chemical structure was confirmed via some characterizations. Afterwards, this synthetic product PA-THAM was employed as an efficient flame retardant to PLA by melt mixing. This binary system showed an improvement in flame retardancy, which was achieved by a combination of heat transfer effect, slight dilution and barrier action. For example, only 3 wt% loading of PA-THAM imparted PLA-based biocomposite LOI value of 25.8% and UL 94 V-0 level, as well as a significant self-extinguishing ability was observed. Besides, the molten viscosity of biocomposite also demonstrated more reduction compared with neat PLA due to the lubrication of PA-THAM, while there was little change in the mechanical properties. 2) PA-THAM and corn pith cellulose (OCC) were combined via in-situ modification and used to prepare a PLA-based biocomposite. After OCC was modified by PA-THAM successfully, which was proved by SEM/ EDS, FTIR, and TGA, the effect of PA-THAM on thermal stability and fire behaviors of PLA-based composite were also investigated accordingly. 5 phr addition of PA-THAM enabled this natural fiber reinforced polymer biocomposite (NPC) to illustrate a 50 °C higher temperature at maximum degradation rate than control sample without additive, and an improvement was also obtained in flame retardant properties with an increase of LOI value, a reduction of PHRR, and more char residue. The predominant flame-retardant mechanism focused on the synergistic effect of PA-THAM and OCC that occurred in condensed phase. Besides, the same level introduction of PA-THAM improved the interfacial affinity between PLA and OCC that maintained good mechanical properties as well. 3) A bio-based thermal insulation material was made from corn pith cellulose, alginate, and bio-efficient flame retardants. After introducing these bio-based additives, the smouldering and flaming combustion behaviors were improved significantly. Compared with the reference sample, thermal insulation particleboard with 8 wt% loading of a mixture of PA-THAM and a sodium borate salt (DOT) increased the initial temperature of smoldering ignition by 70 ºC, and meanwhile, the value of PHRR in flaming combustion decreased by 25.5%. Furthermore, the thermal conductivity was hardly affected, while the temperature at which the maximum thermal degradation occured increased. The correlative flame retardant mechanism was attributed to a synergistic effect from both flame retardants, which promoted a formation of more stable charring layer at initial stage.Los materiales de base biológica ofrecen una alternativa prometedora para aplicaciones en el sector de la construcción, debido a que se trata de materiales biodegradables, renovables y de baja toxicidad. Sin embargo, su capacidad de inflamar y la necesidad de mantener un bajo riesgo frente a incendios en los edificios es un factor esencial para restringir su posterior aplicación. Esta tesis se ha centrado en el desarrollo de materiales de base biológica con buen comportamiento frente al fuego y la investigación de los mecanismos de los retardantes de llama involucrados. La investigación se desarrolló en tres etapas que se detallan a continuación. 1) Partiendo del concepto de base biológica, se seleccionaron PA y THAM como materias primas para sintetizar un nuevo retardante de llama y la estructura química se confirmó mediante la caracterización del compuesto resultante. Posteriormente, este producto sintético PA-THAM se empleó como un retardante de llama eficiente para PLA mediante mezcla fundida. Este sistema binario mostró una mejora en la resistencia al fuego, que se logró mediante una combinación de los efectos de transferencia de calor, ligera dilución y acción barrera. Por ejemplo, con sólo un 3% en peso de carga de PA-THAM se logró un valor de LOI de 25,8% del compuesto de PLA y un nivel UL 94 V-0, así como una capacidad de autoextinción significativa. Además, la viscosidad fundida del biocompuesto también se redujo en relación a la del PLA puro debido a la lubricación ejercida por el PA-THAM. Por otro lado, la adición del retardante ocasionó pocos cambios en las propiedades mecánicas. 2) El retardante basado en PA-THAM y la fracción fina obtenida triturando la médula de maíz (OCC) se combinaron mediante modificación in situ y se usaron para preparar un biocompuesto basado en PLA. La médula de maíz fue modificada con éxito con el PA-THAM, la cual cosa se demostró por SEM / EDS, FTIR y TGA, el efecto de PA-THAM sobre la estabilidad térmica y el comportamiento al fuego del material compuesto a base de PLA también fueron investigados. La adición de 5 phr de PA-THAM permitió a este biocompuesto reforzado con fibras naturales (NPC) alcanzar una temperatura 50 °C más alta en el punto de degradación máximo comparado con la muestra de control sin aditivo. También se obtuvo una mejora en el comportamiento al fuego con un aumento del valor de LOI, una reducción del pico máximo del ritmo de liberación de calor (PHRR), y una mayor formación de residuo carbonizado. El mecanismo ignífugo predominante se centró en el efecto sinérgico del PA-THAM y la OCC que ocurrió en la fase condensada. Además, el mismo nivel de introducción de PA-THAM mejoró la afinidad interfacial entre PLA y OCC que también mantuvo buenas propiedades mecánicas. 3) Se prepararon muestras de un material de aislamiento térmico de base biológica a partir de médula de maíz, alginato y retardantes de llama de origen biológico. La adición del retardante de llama de base biológica logró mejorar significativamente el comportamiento al fuego, y el fenómeno de combustión sin llama (smouldering). En comparación con la muestra de referencia, el panel aislante con una carga de 8% en peso de una mezcla de PA-THAM y una sal de borato de sodio (DOT) aumentó la temperatura inicial a la que se produce la combustión sin llama en 70 ºC y, permitió reducir el valor de PHRR en un 25.5%. Además, la conductividad térmica apenas se vio afectada, mientras que la temperatura a la que se produce el valor máximo de degradación térmica aumentó notablemente. El análisis del mecanismo de acción de los retardantes reveló la existencia de un efecto sinérgico de ambos retardantes de llama, que promovió la formación de una capa de carbonización más estable en la etapa inicial.Postprint (published version

ALIPHATIC SILICA‐EPOXY SYSTEMS CONTAINING DOPO‐BASED FLAME RETARDANTS, BIO‐WASTES, AND OTHER SYNERGISTS

Most industrial applications require polymer‐based materials showing excellent fire performances to satisfy stringent requirements. No‐dripping and self‐extinguishing hybrid silica‐epoxy composites can be prepared by combining tailored sol‐gel synthesis strategies with DOPO‐based flame retardants, bio‐wastes, and other synergists. This approach allows for achieving V‐0 rating in UL‐94 vertical flame spread tests, even using a sustainable route, aliphatic amine as hardener, and low P loadings

Novel phosphorus containing poly(arylene ethers) as flame retardant additives and as reactant in organic synthesis

Due to their outstanding properties, poly(arylene ethers) are useful as toughness modifiers in epoxy resins (EP). Furthermore, these polymers show rather low intrinsic fire risks. According to recent research it has been incorporated that poly(arylene ether phosphine oxides) [PAEPO’s] can further improve the fire behavior. Increasing phosphorous content of the PAEPO can influence the fire behavior too. Fire retardants containing phosphorus – regardless of whether an additive or reactive approach is used – show different mechanisms in the condensed and gas phase. In the present study PSU Control (BPA based polysulfone) with four different PAEPO’s and their corresponding blends with an EP were investigated. All poly(arylene ether phosphine oxides) were synthesized by nucleophilic aromatic polycondensation. The polymers obtained covered a wide range of weight average molar masses (6,000 – 150,000 g/mol) as determined by size exclusion chromatography with multi-angle light scattering detection (MALLS). FTIR, NMR spectroscopy and MALDI-TOF revealed formation of the desired polymer structure of the linear poly(arylene ethers). All polymers were easily soluble in common organic solvents, thus enabling processing from solution.The pyrolysis and the fire retardancy mechanisms of the polymers and blends with epoxy resin (EP) were tackled by means of a comprehensive thermal analysis (thermogravimetry (TG), TG-evolved gas analysis) and fire tests [PCFC, limiting oxygen index (LOI), UL-94, cone calorimeter]. The Mitsunobu reaction of Dimethyl-5-hydroxyisophthalate and a long chain semifluorinated alcohol requires triphenyl phosphine as a reactant. Identical, in some case higher yield was obtained in the usual conditions, with triphenyl phosphine and with trivalent phosphorus containing polymers, which was prepared in solvent free bulk (melt) polymerization technique from trivalent phosphorus monomer and a silylated diphenol in presence of CsF. Purification and the recovery of the final product which is always a big challenge in case of Mitsunobu reaction, was far more easier using polymer compared to triphenyl phosphine. During polymerization there was a possibility to have polymer having repeating unit containing both trivalent phosphorus and phosphine oxide. The trivalent phosphorus content of the polymer can be varied using different molar concentration of CsF