Aashray Narla

Advisor: Prof. Gleb Yushin

will defend his doctoral thesis entitled,

Borohydride-based Solid Electrolytes And Polymer Composite Separators For Lithium-ion Batteries

On

Friday, December 1st at 11:00 a.m.

 Virtually via Zoom

Closed Meeting

Committee:

Prof. Gleb Yushin - School of Materials Science and Engineering (Advisor)

Prof. Preet Singh - School of Materials Science and Engineering

Prof. Faisal Alamgir - School of Materials Science and Engineering

Prof. Seung Soon Jang - School of Materials Science and Engineering

Prof. Alexander Alexeev - School of Mechanical Engineering

Abstract:

Lithium-ion batteries (LIBs) have garnered a lot of interest over the past decade due to their high-energy and power density, prolonged cyclability and long shelf-life. While electric vehicles (EVs) and portable electronics necessitate long range and battery life respectively, we are reaching the limits of energy densities of conventional LIBs that use intercalation active materials and liquid electrolytes. As the current LIB technology additionally relies on highly flammable and toxic electrolytes that are detrimental to the environment, solid electrolytes LIBs have gained more interest over the past years. The solid-state LIBs may offer higher energy densities, lower toxicity and lower flammability compared to their liquid electrolyte equivalents. However, current solid-state electrolytes (SSE) suffer from poor ionic conductivity, low volumetric density, high cost, complicated synthesis, and slow manufacturability at high yields.

In this work, we explore low-melting point anion-substituted/doped borohydride SSEs synthesized by a novel melt-synthesis process capable of being quickly manufacturable at high yields. We systematically investigate the structure and composition of various borohydride SSEs and study the key electrochemical properties such as critical current density to realize their use in all solid-state LIBs. We further fabricate all solid-state LIBs using the melt infiltration method, to assess the borohydride solid electrolyte performance with various LIB active materials. The cycling data of such cells presented similar voltage profiles and capacity retentions to the cells of the same electrodes with liquid organic electrolytes. The promising performance characteristics of such cells will open new opportunities for the accelerated adoption of all solid-state LIBs for safer electric vehicles (EVs).

Additionally to the work on SSEs, we study separators for conventional LIBs. Current LIB technology uses separators made from polyolefins, such as polypropylene and polyethylene, which generally tend to suffer from low porosity, low wettability, and slow ionic conductivity and tend to perform poorly against heat-triggering reactions that may cause potentially catastrophic thermal event issues, such as fire. To overcome these limitations, in this dissertation, we report that a porous composite membrane consisting of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers functionalized with nanodiamonds (NDs) that can realize a more thermally resistant, mechanically robust, and ionically conductive separator. We systematically investigate the role of NDs in the polymer matrix of the membrane to improve the thermal, mechanical, crystalline, and electrochemical properties of the composites. Taking advantages of these mechanistic characteristics, the ND-functionalized nanofiber separator enables high-capacity and stable cycling of lithium anode cells with LiNi0.8Mn0.1Co0.1O2 (NMC811) as the cathode, much superior to those using conventional polyolefin separators in otherwise identical cells.