Skip to main content

Anionic redox processes: A transformational approach for advanced energy materials

Periodic Reporting for period 4 - ARPEMA (Anionic redox processes: A transformational approach for advanced energy materials)

Reporting period: 2020-04-01 to 2021-03-31

+ The problem/ issue being addressed.

Throughout its history, LIB technology has relied on cationic redox reactions as the sole source of energy storage capacity. Back to 2013 our group demonstrated that this was no longer true with the discovery of anionic redox reaction that could lead to materials with drastic increases in energy storage capacity. However, as often the case with new discoveries, the fundamental science at work was remaining to be rationalized and understood for enabling the practical utilization of this new finding. This is what the ARPEMA’s project was aiming to.

+ Importance to the society.

It opens wide new research horizons for advanced electrode materials that will enable to design a new generation of Li-ion batteries with substantial increases in energy storage capacity. They should enable the rapid development of electric transportation and facilitating the use of renewable energy resources. Both of these aspects heavily contribute to lower CO2 emissions and make our lives and our environment more pleasant with a viable legacy to our successors.

+ Overall objective of the project.

Development of a new generation of Li-ion batteries based on sustainable electrode materials enlisting both cationic and anionic redox activities, and exhibiting substantial increases (20 - 30%) in energy storage capacity. Additionally it is aimed to the implementation of the anionic redox concept to Na-ion battery electrodes, a technology with presently only a few well-performing materials offering modest capacities (140 mAh/g), together with the design of water splitting catalysts having the feasibility to surpass current water splitting efficiencies.

+ Conclusion.

Comprehensive research program combining experimental and computational approaches of this relatively nascent concept of anionic redox chemistry for battery applications had been achieved. It covered the theoretical understanding of anionic redox, the materials discovery/design pathway, and specific characterization techniques developed for detecting oxygen redox activity. These new advances have enabled the exploration of many facets that govern the anionic redox process – such as disorder, dimensionality, O/M ratio, hysteresis, voltage fade and stability against O2 release, amongst others.

Shortly, ARPEMA’s achievements, that can be find in the nearly ~50 papers and the ~5 patents that the project has generated, have helped in bringing Li-rich materials close to practical applications, hence letting to envision their use in the next generation of Li-ion batteries that could greatly benefit electric mobility.
Throughout the project duration, key achievements were realised and they are listed below.

+ First direct visualisation of (O-O) peroxo-like dimers in high capacity layered Li-rich oxides by HRTEM is achieved (Science, 2016), hence ending the long remaining controversies about the role of the anionic network.

+ Provided a rationalisation of the anionic redox process by showing that a strong M–(O2) covalence is an absolute condition to ensure high electrochemical reversibility and to prevent O2 gas release from the structure at high states of charge, which is crucial application-wise (Nature Materials, 2016).

+ Studied the poor kinetics of anionic-driven redox process and understood the practical road-blocks of these materials (JES, 2016).

+ Demonstrated (Nature Materials 2017) the feasibility to trigger novel anionic redox process in oxides having three dimensional (3D) rather than two dimensional (2D) crystal structures, thus freeing the structural dimensionality constraints.

+ Designed a novel Li3IrO4 phase that push the limit of the anionic redox activity to 3.7 e- per transition metals – a record among all the cathodes so far investigated (Nature Energy 2016).

+ Uncovered “model” materials based on 4d or 5d metals, having either a 2 or 3 dimensional structures (ex: alpha or beta Li2IrO3). These compounds established a sound scientific platform for rationalizing the design of future anionic-redox-based cathodes and also helped unravelling the origins of practical roadblocks in Li-rich cathodes (Nature Materials, 2018, “Fundamental understanding and practical challenges of anionic redox activity in Li-ion batteries”).

+ Isolated a Na-rich phase Na2IrO3 phase which can reversibly cycle 1.5 Na+ per formula unit while not suffering from oxygen release nor cationic migrations. This work published in Chemistry of Materials turns out to be an impetus for the design of high energy Na-rich materials based on more sustainable elements than Ir as we are presently investigating.

+ Extended anionic redox to chalcogenides Li1.13Fe0.33Ti0.54S2 (LTFS) phase (Nature Energy 2020) with minimized voltage fade and hysteresis that presently serves as benchmark positive electrode materials for solid state batteries.

+ Successfully extended anionic redox to Na-based materials and prepared the first and unique so far O3-type NaLi1/3Mn2/3O2 layered oxide showing high sustained reversible capacity with no voltage fade while being moisture insensitive unlike other Na-based compounds (Nature Materials 2021).

+ Apart from battery materials, ARPEMA has shown the feasibility of extending the anionic redox process to catalysts for water splitting by establishing for the first time the correlation existing between the OER activity and stability for perovskites when triggering the surface oxygen redox (Nature Energy 2017).

+ Finally, beside materials and theoretical developments, innovative developments of new analytical techniques were also achieved. Some of them are as follows,

i) A new and versatile cell to conduct specific operando electrochemical quartz crystal microbalance (EQCM) measurements (Applied Materials & Interfaces (2020)).

ii) Demonstration for the first time of an optical calorimeter based on the use of optical Fiber Bragg Grating (FBGs) to monitor chemical and thermal events associated to the cycling of Li-rich oxides/sulfides based batteries (Nature Energy, (2020).

iii) The development of specific electrochemical cells for assembling and testing solid-state batteries. Some of these tools together with the help of an ERC-PoC-2016 had led to creation of a company, SPHERE ENERGY.

Altogether, these advances published in high impact journals (Nature materials, Science) have been widely cited and received unsolicited coverage in press worldwide.
Exciting results were obtained some of which be beyond our initial expectations. Anionic redox process, first described in layered compounds is generalized to three dimensional oxides, hence, widely expanding the crystal chemical landscape for designing high energy density electrodes. Discovery of a new phase Li3IrO4 showing the highest capacity (3.6 e- per Ir metal) ever reported for any positive electrode materials till now. Application-wise, such new class of materials having exacerbated capacity enables the next generation of Li-ion batteries with substantial increases (20-30%) in energy storage capacity provided we could replace Ir by low cost and abundant 3d chemical elements.

Moreover, ARPEMA had opened a wide range of research opportunities that the group is presently considering by the launching of new projects dealing with sensing and others. None of this could have happened without this “ERC advanced Grant” project, a bright European initiative.
Exploration of anionic redox in Li-rich sulphides
Exploration of anionic redox in Na-layered oxieds
Strategy to activate anionic redox
Li-rich layered oxide: Materials exploration
Studies on 3dimensional compounds: Beta-Li2IrO3
Structural evolution of Li3IrO4
Effect of the rate capability of Li2Ru0.75Sn0.25O3
Direct observation of O-O dimers (Li2IrO3)