No description available.

The a.c. conductivity of the solid electrolyte beta-alumina with blocking Au electrodes has been examined by complex plane analysis using the complex impedance (Z*), admittance (A*), modulus (M*) and permittivity (epsilon*) formalisms. The electrode response which gives rise to the characteristic "spikes" in the Z* plots is attributed to a highly resistive layer on the surface of beta-alumina. This is found on single crystal and polycrystalline materials, and is sensitive both to the effects of polishing and the uptake of water vapour. Water vapour does not affect the bulk properties. For the first time, both the conductivity and the modulus spectra of single crystal beta"-alumina have been reported. It is confirmed that beta"-alumina has a much higher activation energy (~27kJ/mole) than beta-alumina (16.0kj/mole) and thus has a lower conductivity at lower temperatures (100°C). On this basis, an attempt has been made to explain the behaviour of the (commercial) polycrystalline sinters which are mixtures of beta and beta" phases. While the grain boundary activation energy remains constant at ~ 26kJ/mole, the bulk activation energy varies with beta/beta" content. The mixtures of approx 50-70% beta" content have the lowest bulk activation energy. These effects may be related in some way to the method of charge compensation, and in particular to the interstitial oxygen content (Oi2-). A "mixed-alkali" effect has been discovered in Na/Ag beta-aluminas which is remarkably similar to the effects found in glass. Both conductance minima and modulus (M") peak "narrowing" are observed. The results add some support to the weak electrolyte theory of beta-alumina, and also offer an interesting new exception to Jonscher's "universal" dielectric behaviour.

No description available.

The ionic conductivity of the lithium ionic conductor, Li5La3Ta2O12, is studied in an attempt to better understand the intrinsic bulk ionic conductivity and extrinsic sample dependent contributions to the ionic conductivity, such as grain boundary effects and the electrode-electrolyte interface. To characterize the material, traditional AC impedance spectroscopy studies were performed as well novel in-situ nanoscale transport measurements. To perform the nanoscale measurements, higher quality samples were required and new synthesis techniques developed. The results of these new synthesis techniques was samples with higher densities, up to 96% of theoretical, and slightly higher room temperature ionic conductivity, 2x10^−5 S/cm. By combining the AC impedance spectroscopy results and in-situ nanoscale transport measurements from this study and prior reported results, as well as introducing models traditionally used to analyze supercapacitor systems, a new interpretation of the features seen in the AC impedance spectroscopy studies is presented. This new interpretation challenges the presence of Warburg Diffusion at low frequencies and the offers a new interpretation for the features that have been traditionally associated with grain boundary effects.

京都大学 / 新制・課程博士 / 博士(人間・環境学) / 甲第23286号 / 人博第1001号 / 新制||人||236(附属図書館) / 2020||人博||1001(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 内本 喜晴, 教授 田部 勢津久, 教授 高木 紀明 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(人間・環境学) / 甲第21432号 / 人博第870号 / 2018||人博||870(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 内本 喜晴, 教授 田部 勢津久, 教授 吉田 鉄平 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

<p>Li-ion batteries (LIBs) are currently pervasive across portable electronics and electric vehicles and are on the ascent for large-scale applications such as grid storage. However, commercial LIBs based on intercalation chemistries are inching toward their theoretical energy density limits. Consequently, the rapidly growing demands of energy storage have necessitated a recent renaissance in exploring battery systems beyond Li-ion chemistry. Next-generation batteries that utilize Li metal as the anode can improve the energy density and power density of LIBs. Despite the theoretical promise, the commercialization of metal-based batteries requires overcoming several hurdles, stemming from the unstable nature of Li in liquid electrolytes. Upon repeated charging, the metal anode undergoes unrestricted growth of dendrites, devolving to a thermal runaway in extreme circumstances. By replacing the organic liquid electrolyte with a non-flammable solid electrolyte, solid-state batteries (SSBs) can potentially provide enhanced safety attributes over liquid electrolyte cells. Upon pairing of solid electrolytes with a Li metal anode, such systems present the unique possibility of engineering batteries with high energy density and fast charging rates. However, there are a number of technical challenges and fundamental scientific advances necessary for SSBs to achieve reliable electrochemical performance. The formation of dendritic morphologies during charging and the loss of active area at the anode-electrolyte interface during discharging are two critical limitations that need to be addressed.</p> <p>In this thesis, the morphological stability of the Li metal anode is examined based on the mechanistic interaction of electrochemical reaction, ionic transport and surface self-diffusion, that is further dependent on aspects including the thermal field and electrolyte composition. The origin of electrochemical-mechanical instability and metal penetration due to heterogeneities in solid-state electrolytes such as grain boundaries will be analyzed. The phenomenon of contact loss at solid-solid interfaces due to the competing interaction between electrochemical dissolution and Li mechanics will be studied. Lastly, the mechanistic attributes governing the thermal stability of solid-solid interfaces in solid-state batteries will be examined. Overall, the dissertation will focus on understanding the fundamental mechanisms underlying the evolution of solid-liquid and solid-solid interfaces in energy storage and derive potential design guidelines toward achieving stable morphologies in metal-based batteries.</p>

A solid electrolyte is a crucial component of any solid state battery. Polymer gel electrolytes have received increasing attention in recent years due to their high ionic conductivity, flexibility, and improved safety. However, a general tradeoff usually exists between the mechanical properties and ionic conductivity in such materials. Molecular ionic composites (MICs) are a new type of rigid polymer gel electrolyte based on ionic liquids (ILs) and a double helical rigid-rod polyamide, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT). MICs have high ionic conductivity, high thermal and electrochemical stability, and widely tunable and high tensile modulus even at relatively low polymer content. MICs show great promise as solid electrolytes for solid state batteries. This dissertation describes the preparation and characterization of MIC electrolyte membranes. These transparent, flexible, and tough membranes are prepared through a convenient solvent casting process. A large variety of ILs, including both hydrophilic and hydrophobic examples, are suitable to prepare MIC electrolyte membranes by adjusting the solvents used in the casting process. The prepared membranes show a biphasic internal structure consisting of a PBDT-rich “bundle” phase and an IL-rich “puddle” (interconnected fluid) phase. Similar to the bulk MIC ingots prepared previously through an interfacial ion exchange process, the MIC membranes also have high ionic conductivity and tensile modulus at low polymer content. A MIC membrane composed of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr₁₄TFSI), LiTFSI, and PBDT in a mass ratio of 8:1:1 is tested as a solid electrolyte for lithium metal batteries. This electrolyte membrane shows high ionic conductivity and high rigidity. The shear storage modulus of this MIC electrolyte membrane only decreases by 35% when heated to 200 °C from room temperature, suggesting great mechanical stability at high temperatures. The electrolyte membrane is successfully used as solid electrolyte for a Li/LiFePO₄ battery working over a large temperature range from 23 to 150 °C, and the discharge capacity retention of the cell is as high as 99% after 50 cycles at 150 °C. By replacing the IL in the MIC with a charge-neutral liquid, single-ion-conducting polymer gel electrolyte composed of PBDT and polyethylene glycol (PEG) oligomer are obtained. Similar to the MICs, these single-ion-conducting materials also have high Young’s modulus and biphasic internal structures. This study reveals that the counter ion (Li⁺ or Na⁺) of the PBDT has a major effect on both the ionic conductivity and modulus of the materials. Due to the stronger intermolecular interactions, LiPBDT-PEG demonstrates lower ionic conductivity but higher Young’s modulus. This dissertation also evaluates the viability of rigid PBDT as a polymer binder for electrodes. Aqueous solution-processed LiFePO₄ electrodes with only 3 wt% PBDT demonstrate stable cycling over 1000 cycles without obvious capacity decay, and the rate capacity of these aqueous solution-processed electrodes are comparable to the electrodes prepared with conventional poly(vinylidene difluoride) (PVDF) as the binder, suggesting PBDT can serve as a potential electrode binder for commercial applications. / A solid electrolyte is a crucial component of any solid state battery. Polymer gel electrolytes have received increasing attention in recent years due to their high ionic conductivity, flexibility, and improved safety. However, a general tradeoff usually exists between the mechanical properties and ionic conductivity in such materials. Molecular ionic composites (MICs) are a new type of rigid polymer gel electrolyte based on ionic liquids (ILs) and a double helical rigid-rod polyamide, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT). MICs have high ionic conductivity, high thermal and electrochemical stability, and widely tunable and high tensile modulus even at relatively low polymer content. MICs show great promise as solid electrolytes for solid state batteries. This dissertation describes the preparation and characterization of MIC electrolyte membranes. These transparent, flexible, and tough membranes are prepared through a convenient solvent casting process. A large variety of ILs, including both hydrophilic and hydrophobic examples, are suitable to prepare MIC electrolyte membranes by adjusting the solvents used in the casting process. The prepared membranes show a biphasic internal structure consisting of a PBDT-rich "bundle" phase and an IL-rich "puddle" (interconnected fluid) phase. Similar to the bulk MIC ingots prepared previously through an interfacial ion exchange process, the MIC membranes also have high ionic conductivity and tensile modulus at low polymer content. A MIC membrane composed of 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr14TFSI), LiTFSI, and PBDT in a mass ratio of 8:1:1 is tested as a solid electrolyte for lithium metal batteries. This electrolyte membrane shows high ionic conductivity and high rigidity. The shear storage modulus of this MIC electrolyte membrane only decreases by 35% when heated to 200 °C from room temperature, suggesting great mechanical stability at high temperatures. The electrolyte membrane is successfully used as solid electrolyte for a Li/LiFePO4 battery working over a large temperature range from 23 to 150 °C, and the discharge capacity retention of the cell is as high as 99% after 50 cycles at 150 °C. By replacing the IL in the MIC with a charge-neutral liquid, single-ion-conducting polymer gel electrolyte composed of PBDT and polyethylene glycol (PEG) oligomer are obtained. Similar to the MICs, these single-ion-conducting materials also have high Young's modulus and biphasic internal structures. This study reveals that the counter ion (Li+ or Na+) of the PBDT has a major effect on both the ionic conductivity and modulus of the materials. Due to the stronger intermolecular interactions, LiPBDT-PEG demonstrates lower ionic conductivity but higher Young's modulus. This dissertation also evaluates the viability of rigid PBDT as a polymer binder for electrodes. Aqueous solution-processed LiFePO4 electrodes with only 3 wt% PBDT demonstrate stable cycling over 1000 cycles without obvious capacity decay, and the rate capacity of these aqueous solution-processed electrodes are comparable to the electrodes prepared with conventional poly(vinylidene difluoride) (PVDF) as the binder, suggesting PBDT can serve as a potential electrode binder for commercial applications. / Doctor of Philosophy / Solid state batteries are widely considered as the pathway to next-generation high performance batteries. In a solid state lithium battery, the liquid organic carbonate electrolyte is replaced with a solid electrolyte. Polymer gel electrolytes are a type of potential solid electrolyte that have been widely studied in recent decades. This dissertation describes the application of a rigid polymer in preparing polymer gel electrolytes. This highly charged and rigid polymer is a water-soluble polyamide known as PBDT with a double helical structure akin to DNA. Through a modified solvent casting process, a new type of polymer gel electrolyte, known as molecular ionic composite (MIC), is prepared using PBDT and various ionic liquids. Extra salt (which can contain lithium) can also be incorporated into the MIC membrane. This type of new polymer gel electrolyte is rigid with high tensile modulus even at high temperatures and low polymer (PBDT) content. MIC membranes are used as solid electrolytes for lithium metal batteries working over a wide temperature range from 23 to 150 °C. A rigid polymer gel electrolyte can also be obtained by replacing the ionic liquids in MICs with polyethylene glycol. Besides the application in preparing solid electrolytes, PBDT is also evaluated as a polymer binder for aqueous processed electrodes. Preliminary study reveals that PBDT holds great potential for a range of commercial energy storage applications.

京都大学 / 新制・課程博士 / 博士(人間・環境学) / 甲第23995号 / 人博第1047号 / 新制||人||245(附属図書館) / 2022||人博||1047(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 内本 喜晴, 教授 中村 敏浩, 教授 陰山 洋, 教授 雨澤 浩史 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

京都大学 / 新制・課程博士 / 博士(人間・環境学) / 甲第23287号 / 人博第1002号 / 新制||人||236(附属図書館) / 2020||人博||1002(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 内本 喜晴, 教授 田部 勢津久, 准教授 戸﨑 充男 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM