Understanding the Role of Chemically Preintercalated Ions, Doping and Heterointerfaces in MXene-Derived Oxide Electrodes for Aqueous Zn-Ion Batteries

NON-TECHNICAL DESCRIPTION:

Energy storage devices, such as batteries, are essential for achieving clean energy and a sustainable future. Lithium-ion batteries (LIBs), which are widely used in portable electronics, electric vehicles, and grid-scale energy storage, present safety issues related to fire hazard and raise concerns due to the limited abundance of lithium. Aqueous zinc-ion batteries (AZIBs) offer an attractive alternative to LIBs because of their high performance characteristics, low cost, environmental friendliness, and safety.

However, the widespread adoption of AZIB technology is hindered by the need to develop cathode materials that can efficiently insert and extract zinc ions while remaining stable over many battery discharge/charge cycles. This project, supported by the Ceramics program in the Division of Materials Research at NSF, explores strategies to improve the cycling stability of layered vanadium oxide cathodes in AZIBs for both slow and fast battery operations.

These strategies include the incorporation of stabilizing cations in the interlayer region of the vanadium oxide structure, the partial replacement of vanadium with another transition metal in the layer structure, and the formation of a tight oxide/carbon contact on the surface or within the volume of the synthesized particles. These approaches are enabled by the use of MXenes - transition metal carbide nanoflakes - as precursors in a synthesis method called chemical preintercalation, developed by the PI.

This interdisciplinary project engages and educates students with diverse backgrounds by offering research opportunities in electrochemical energy storage at undergraduate and graduate levels. It also integrates topics on ceramic material transformations, energy storage, and in situ electrochemical characterization into the engineering curriculum through courses taught by the PI.

Additionally, this project enriches outreach programs by creating an activity based on coloring outline images prepared from real microscopy images of synthesized materials. The PI also teaches students how to digitally color microscopy images to create artistic illustrations and organizes a competition featuring these images at her home institution.

TECHNICAL SUMMARY:

This project, supported by the Ceramics program in the Division of Materials Research at NSF, aims to mitigate performance degradation of chemically preintercalated bilayered vanadium oxide (BVO) cathodes in aqueous zin-ion batteries (AZIBs) caused by limited ion diffusion, low electrical conductivity, dissolution in the electrolyte, and formation of unwanted by-products during cycling. The goal of this project is to develop new ceramic materials with tunable structures that exhibit high zinc ion storage capability, rapid electron and ion transport, and enhanced electrochemical stability.

The goal is achieved by testing the hypothesis that high capacity, long cycle life and fast charging can be delivered by MXene-derived (MD) vanadium oxide electrodes in AZIBs. This is pursued through chemically preintercalated ions (CPI), doping at vanadium sites, and controllable heterointerfaces. Using MXene nanoflakes as precursors allows for unique morphologies, structures and chemical compositions, leading to enhanced zinc ion diffusion, increased electrical conductivity, and suppressed electrode dissolution.

The research addresses three objectives to overcome limitations of layered vanadium oxide cathodes in AZIBs: (1) Enhance Zn2+-ion diffusion by controlling interlayer spacing via chemical preintercalation of ions, using MXene nanoflakes for unique 2D morphology and improved electrochemical stability; (2) Suppress V–O cathode dissolution by doping vanadium sites in the BVO structure with another transition metal, achieved using solid-solution MXenes; (3) Further advance electrochemical stability and rate capability through the formation of oxide/carbon heterointerfaces and/or conductive carbon surface-protection layers by tuning MXene monolayer thickness. The mechanism of electrochemical stabilization at various cycling rates is established via a comprehensive suite of in-situ electrochemical characterization approaches, including XRD, SEM and pH measurements.

The insights into ion diffusion coefficients, charge storage mechanism and evolution of electrodes during electrochemical cycling, obtained in this project, enable the design of cathode materials with enhanced energy/power storage capabilities and electrochemical stability in AZIBs.

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.