Non-equilibrium metal oxides via reconversion chemistry in lithium-ion batteries

Abstract

Binary metal oxides are attractive anode materials for lithium-ion batteries. Despite sustained effort into nanomaterials synthesis and understanding the initial discharge mechanism, the fundamental chemistry underpinning the charge and subsequent cycles—thus the reversible capacity—remains poorly understood. Here, we use in operando X-ray pair distribution function analysis combining with our recently developed analytical approach employing Metropolis Monte Carlo simulations and non-negative matrix factorisation to study the charge reaction thermodynamics of a series of Fe- and Mn-oxides. As opposed to the commonly believed conversion chemistry forming rocksalt FeO and MnO, we reveal the two oxide series topotactically transform into non-native body-centred cubic FeO and zincblende MnO via displacement-like reactions whose kinetics are governed by the mobility differences between displaced species. These renewed mechanistic insights suggest avenues for the future design of metal oxide materials as well as new material synthesis routes using electrochemically-assisted methods.

Recovering local structure information from high-pressure total scattering experiments

“…PDFs of composite systems such as amorphous solid dispersions and battery materials have been successfully separated into their constituent components using nonnegative matrix factorization (NMF) methods (Geddes et al, 2019;Hua et al, 2021). Ordinarily, this approach recovers the relative scattering contributions of individual components to a series of composite PDFs, with continually evolving relative concentrations.…”

Multivariate Analysis of Disorder in Metal–Organic Frameworks

“…49 Subsequent studies have included the cycling of lithium-ion batteries, the interface between Fe and Fe3O4 and pharmaceutical amorphous solid dispersions. 33,34,48,50 In the majority of cases, PDF studies coupled with PCA focus on phase mixtures and it is principal components which contain atom-atom correlations that have…”

“…27 PDF analysis has been used to provide insight into the negative thermal expansion behaviour in ZrW2O8, the structure of metal oxide nanoparticles, in-situ formation of hybrid materials, operando studies on battery materials and, of course, studies on structural disorder. [28][29][30][31][32][33][34][35][36] From a practical perspective, advances in instrumentation mean the bottleneck now lies in data analysis. While many approaches towards PDF analysis exist, such as small-and large-box modelling, differential analysis and even machine learning, it remains difficult to readily characterise the processes by which disorder is often incorporated within framework materials, such as structural collapse or melting.…”

Extracting interface correlations from the pair distribution function of composite materials

“…In this study, we show that this interface contribution to the PDF (we call it the 'iPDF') can actually be extracted using non-negative matrix factorisation (NMF) analysis 34 -a method only recently applied to PDF data as a means of deconvolving the function into its individual component factors. [35][36][37] We begin by establishing proof-of-concept, using idealised PDF data generated from suitably-constructed models of the Fe∥Fe 3 O 4 interface. We then report experimental X-ray total scattering measurements for controlled corrosion of polycrystalline Fe powder.…”