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  • PhD Defense

    Tue, Oct 23, 2018 @ 11:00 AM - 12:00 PM

    Mork Family Department of Chemical Engineering and Materials Science

    Conferences, Lectures, & Seminars

    Speaker: Mr. Anyi Zhang , PhD Student, CHE

    Talk Title: 'Nanostructure Design of Sulfur Cathodes and Lithium Metal Anodes for Lithium Ion Batteries

    Abstract: Lithium ion batteries (LIBs) have been successfully used in portable electronics and electric vehicles for many years. Although the demand for high energy density keeps increasing, the existing commercial LIB systems are getting close to their theoretical capacity limits. In order to push the energy density to an even higher level, lithium sulfur (Li-S) batteries attract a lot of attention due to their high energy density and low cost. In this thesis, I will discuss the current challenges we are facing in Li-S battery development and our proposed solutions to address those issues using nanostructure design.

    I will first present our accomplishment to enhance the S cathode performance. We have developed a scalable and inexpensive design for S cathode by capping a flexible gel polymer / carbon nanofiber (CNF) composite membrane onto a free-standing and binder-free CNF + Li2S6 cathode, thus forming a three-dimensional (3D) structural design. While the CNF network was used as the current collector and S holder to overcome the insulating nature and volume expansion of S, the composite membrane composed of a gel polymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and CNF additive was used as an interlayer to trap polysulfides and recycle remaining S species, leading to high specific capacity and long cycle life.

    Next, I will talk about our achievement for stable Li metal anodes. We have demonstrated a distinctive design for dendrite-free deposition of Li by modifying the Cu current collector with a 3D CNF network. Due to the large surface area and high conductivity of the CNF network, Li metal can insert into and deposit onto CNF directly and no dendritic Li metal was observed, leaving a flat Li metal surface. The scalable preparation method and impressive results achieved here demonstrated the potential of applying our design in the development of dendrite-free Li metal anodes in future.

    In addition, I will also present my research to further improve the performance of Li metal anodes. We have proposed a novel design of 3D interconnected graphene (IG) framework synthesized with the help of nickel (Ni) microspheres for stable Li metal anodes. The as-prepared IG framework consisted of multiple stacks of two-dimensional (2D) graphene layers and plenty of hollow graphene microspheres in between, and thus provided protective layers on the top to suppress lithium dendrites, sufficient surface area to reduce the effective current density, as well as ion channels for fast Li transport. This strategy of vertically stacking 2D materials provides a novel approach towards dendrite-free Li metal anodes for the next-generation energy storage systems.

    Host: Dr. Chongwu Zhou

    Location: Ronald Tutor Hall of Engineering (RTH) - 306

    Audiences: Everyone Is Invited

    Contact: Karen Woo/Mork Family


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