Materials Development for All-Solid State Battery Electrolytes

solid electrolytes;Materials Science and Engineering;Engineering;Materials Science and Engineering

Wang, WeiminLaine, Richard M ;

University of Michigan

关键词: solid electrolytes;    Materials Science and Engineering;    Engineering;    Materials Science and Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/137106/weimin_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Solid electrolytes in all solid-state batteries, provide higher attainable energy density and improved safety. Ideal solid electrolytes require high ionic conductivity, a high elastic modulus to prevent dendrite growth, chemical compatibility with electrodes, and ease of fabrication into thin films. Although various materials types, including polymers, ceramics, and composites, are under intense investigation, unifying design principles have not been identified.In this thesis, we study the key ion transport mechanisms in relation to the structural characteristics of polymers and glassy solids, and apply derived material design strategies to develop polymer-silica hybrid materials with improved electrolyte performance characteristics. Poly(ethylene) oxide-based solid electrolytes containing ceramic nanoparticles are attractive alternatives to liquid electrolytes for high-energy density Li batteries. We compare the effect of Li1.3Al0.3Ti1.7(PO4)3 active nanoparticles, passive TiO2 nanoparticles and fumed silica. Up to two orders of magnitude enhancement in ionic conductivity is observed for composites with active nanoparticles, attributed to cation migration through a percolating interphase region that develops around the active nanoparticles, even at low nanoparticle loading. We investigate the structural origin of elastic properties and ionic migration mechanisms in sodium borosilicate and sodium borogermanate glass electrolyte system. A new statistical thermodynamic reaction equilibrium model is used in combination with data from nuclear magnetic resonance and Brillouin light scattering measurements to determine network structural unit fractions. The highly coordinated structural units are found to be predominantly responsible for effective mechanical load transmission, by establishing three-dimensional covalent connectivity. A strong correlation exists between bulk modulus and the activation energy for ion conduction.We describe the activated process in glasses as involving a jump by the migrating cation and transient reversible isotropic displacement of atoms in the immediate vicinity, and express the activation energy as a sum of Coulomb and elastic terms. By fitting our experimental data to this model, we find that the number of affected atoms in the vicinity ranges between 20 and 30.Furthermore, elastic deformations in ion jumping are almost purely hydrostatic and hardly shear. Considering that the energy required for the cation jump is made available by concentrating thermal phonons at the jump site, we establish a relationship between structural stiffness and activation energy. Moreover, the more atoms that partake in the cation jump, the more degrees of freedom for atomic motion can be relied upon to achieve the required net outward expansion to facilitate the passage of the jumping cation, lowering the activation energy.To combine the flexibility of polymers and the good mechanical and electrochemical properties of silica, we use sol-gel methods for fabricating silica-based hybrid organic-inorganic electrolytes. Polyethylene glycol is covalently grafted onto the silica backbone as the organic filler that provides the environment for ion conduction. We developed synthesis methods in which grafting and polycondensation occur concurrently, or the grafting occurs after the silica backbone has formed. Small angle x-ray scattering measurements reveal that different structures are achieved depending on the method used.The two-step procedure allows for a larger amount of conducting polymer to be embedded into network pores than in the one-pot method. This greatly enhances the ionic conductivity without sacrificing mechanical stability afforded by the continuous silica backbone. Here we provide a cumulative account of a systematic materials design efforts, in which we sequentially implement several important design aspects to identify their respective importance and influence on the materials performance characteristics.