Open framework structure materials for energy storage applications

Lead Research Organisation: University of Oxford
Department Name: Materials

Abstract

This project will focus on the synthesis and characterization (both structural and electrochemical) of Prussian Blue analogue (PBAs) materials, with a focus on their applications for energy storage.

The fraction of energy production from renewable sources is increasing. Their intermittent nature requires energy storage solutions on the grid scale to smooth differences in supply and demand. These differences arise on the second, diurnal and seasonal time scales. Additionally, improvements in portable battery technology are required due to the increase in prevalence of electric vehicles and portable electronics. Current electrochemical energy storage technology is mature with only incremental improvements being made. Novel battery chemistries need to be pursued in order to make the necessary step change advances.

Prussian Blue analogue materials have an open framework crystal structure which leads to them having attractive electrochemical properties. They have large interstitial sites connected by wide pathways. They display fast ion insertion and extraction kinetics and good cycling stability, due to minimal lattice strain on ion insertion. Moreover the materials are based on cheap earth abundant, non-toxic elements. Previous work has demonstrated extremely long cycle life of tens of thousands of cycles and also the ability of the material to insert a wide selection of cations, including both di- and trivalent cations.

Within the material there are two distinct crystallographic sites occupied by transition metal species. In Prussian Blue both these species are iron. Prussian Blue analogues are synthesised when one, or both, of these sites are exchanged for a different transition metal while retaining the same open framework crystal structure. An advantage of working with this material system is the vast range of compositions possible when exchanging these cations. This leads to the ability to control and tailor the materials properties to specific applications.
A simple co-precipitation method in an aqueous solvent will be used to synthesise a wide variety of PBAs . Initial structural, chemical and morphological characterisation will be carried out using X-ray powder diffraction (XRD), inductively coupled plasma spectroscopy (ICP) and scanning electron microscopy (SEM). The materials electrochemical properties will be studied using a range of techniques including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic cycling.

A range of materials will be investigated for their applicability as cathodes, anodes and solid electrolytes in electrochemical cells based on Na+, Li+ and K+ insertion ions. Compositions will be optimised leading to the eventual goal of an electrochemical cell where all major components are Prussian Blue analogues based.

The EPSRC research theme is Energy.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509711/1 01/10/2016 30/09/2021
1802884 Studentship EP/N509711/1 01/10/2016 31/03/2020 Samuel Wheeler
 
Description My project has been focusing on developing low potential (anode) Prussian blue analogue (PBA) materials for sodium- and potassium-ion batteries. I have successfully identified and characterised manganese hexacyanochromate as a low potential PBA material. This was the first report of this material and was published in Chemistry of Materials. After this work I focussed on other low potential PBA materials that can store more charge (for higher energy density batteries) than manganese hexacyanochromate. I have found that chromium hexacyanochromate is the most promising material. To make this material I have had to develop a novel synthesis method and a thermodynamic model of PBA synthesis. This work will be published shortly and is widely applicable, to areas of research outside low potential PBA materials for batteries.
Exploitation Route I have synthesised and characterised manganese hexacyanochromate and chromium hexacyanochromate as battery materials. Specifically, this work has move the research into low potential PBA materials forward and closer to making a full PBA battery. This is the first reported synthesis of chromium(III) hexacyanochromate(III). During this research I have, also, developed better models for the synthesis of this family of materials that have wider applicability. PBAs have interesting magnetic, optical and gas adsorption properties, for which my work has contributed to considerably.
Sectors Energy

 
Description Batteries made using Prussian blue analogues (PBA) as the active materials have potential to be very cheap and long lived making them ideal for stationary grid-level energy storage. There have been efforts to commercialise batteries based on PBAs and my research has potential to improve the performance of these batteries making them more commercially attractive.
First Year Of Impact 2019
Sector Chemicals,Energy
Impact Types Economic