Collaborative Research: Thermodynamics and Ion Transport in Hybrid Organic-Inorganic Block Copolymer Electrolytes

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

NONTECHNICAL DESCRIPTION: Life is increasingly intertwined with electrochemical energy storage, mainly in the form of lithium batteries. They are integral to cellphones, laptops, scooters, electric vehicles, homes, solar installations, and even airplanes. But these basic devices have potential safety hazards because they carry within a highly flammable liquid that has led to explosions and fires. Building an intrinsically safe rechargeable lithium battery remains an unmet challenge, particularly in the development of a nonflammable electrolyte (the material that allows the flow of electrical charge in the battery) to replace the flammable organic liquid electrolyte in current lithium batteries. Polymer electrolytes offer a promising alternative to the flammable liquid. All previous studies have considered polymers made from organic building blocks. The proposed work begins with a novel approach: the synthesis of a hybrid polymer that comprises both organic and inorganic building blocks. The polymer spontaneously forms 10-nanometer-wide alternating organic and inorganic layers (a human hair is 100,000 nanometers wide). This material had very low flammability. The organic layers conduct the lithium ions while the inorganic layers provide mechanical rigidity to the polymer electrolyte, a property that is necessary to keep the two battery electrodes from touching and short-circuiting the battery. The planned work examines the relationship between layer formation and lithium-ion motion through the composite electrolyte. The PIs collaborating on this project will also be working on diversity-related initiatives on the UC Berkeley campus, on organizing public lectures on scientific subjects aimed at high school students in Brooklyn, and on providing multidisciplinary training to undergraduate and graduate students at their institutions. TECHNICAL DESCRIPTION: The proposed work focuses on mixtures of hybrid organic-inorganic block copolymers and a lithium salt. Functionalized polyhedral oligomeric silsesquioxane (POSS) particles are covalently bonded to the inorganic block; the organic block is polyethylene oxide (PEO). The hybrid block copolymers (PEO-POSS) will be synthesized using nitroxide-mediated radical polymerization with functionalized PEO as the macro-initiator. Early results indicate that the phase behavior of pure PEO-POSS block copolymers is as expected: increasing temperature leads to an order-to-disorder transition. In contrast, salt-containing PEO-POSS mixtures exhibit a disorder-to-order transition with increasing temperature. The effect of block ratio, chain length, and POSS functionality will be studied by a combination of depolarized light scattering, X-ray scattering, and electron tomography. Measurements will be made over a wide range of block copolymer compositions, salt concentration, and annealing conditions. The effect of morphology on ion transport will be measured by ac impedance spectroscopy. The intellectual merit of the proposed work will be the study of the thermodynamic interactions and ion transport in an emerging class of hybrid nanostructured polymers comprising fully organic polymers and polymers with covalently-bonded inorganic nanoparticles; the present quantitative understanding of these properties is largely restricted to all-organic chains. . This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.