Advanced Characterisation Methods
current research topics
Electrochemical Energy Storage
Electrochemical energy storage (EES) devices are crucial to advance into a more sustainable and decarbonised future powered by renewables such as solar radiation or wind. Moreover, improved EES systems are required to enable the increasing demand of hybrid electric vehicles, plug-in vehicles and all-electric vehicles and in the development of modern portable electronic devices such as laptops and smartphones.
These devices store electrical energy using chemical (redox) reactions, benefitting from the fact that both types of energy share the same carrier, the electron. Among the different types of EES devices, rechargeable batteries are one of the most promising technologies, given their ability to store large amounts of energy. The importance of these devices is reflected in the awarding of the 2019 Nobel Prize in Chemistry to the "fathers" of the Li-ion battery: Whittingham, Goodenough and Yoshino.
A typical battery consists of two electrodes (cathode and anode) separated by an ion-conducting media (the electrolyte). Upon charge, ions travel from the cathode to the anode through the electrolyte while electrons travel through the external circuit in the same direction, creating a flow of current. The opposite occurs during discharge, releasing the stored energy.
One of our main research goals is to advance understanding of the structure-property relationships observed in battery materials to improve battery performance. Our research employs a range of synthetic methods and characterisation techniques which include diffraction, spectroscopy and microscopy techniques at different length scales. Part of our research is also developed in national science facilities such as the Diamond Light Source and the ISIS neutron spallation source in Didcot (UK), the European Synchrotron Radiation Facility (ESRF) in Grenoble (France) and the Australian Synchrotron. Our current research focusses around the study of various rechargeable battery systems, which are detailed below. Go to Publications to find more about our works in this area.
Next generation cathode materials for Li-ion batteries
In lithium-ion batteries (LIBs), the anode consists of a carbon material (commonly graphite) which can store lithium ions within the carbon layers. On the other hand, layered transition metal oxides are widely used as cathode materials due to their large channels for lithium ion diffusion. These typically exhibit lower energy storage capability than anode materials, limiting the overall energy density in LiBs. This implies the use of higher mass cathode loadings, increasing the cost of the battery. Therefore, considerable research efforts are needed to increase the energy density of these materials.
We are currently developing several strategies to improve the energy-density in Co-free high-voltage spinel materials which involve: 1) the creation of novel electrode architectures such as core-shell type and sandwich-like structures; 2) the development of alternative synthetic routes to control particle size and morphology in these materials; and 3) structural modification via doping and off-stoichiometric compound (Li-excess and oxygen deficient compounds).
In recent years, there has been a growing interest around the potential for replacing commercial Li-ion batteries (LIBs) with more cost-effective Na-ion batteries (NIBs) in a wide range of applications, owing to the abundance of sodium resources. To our advantage, sodium and lithium exhibit similar chemical behaviour, which allow us to extrapolate the acquired knowledge gained on LIBs in the past thirty years and apply it in NIBs. NIBs are ideal for stationary energy storage applications due to their low-cost, safety and functionality over a wide temperature range, especially nowadays that the world in increasingly relying on renewable energy sources. Nevertheless, there are challenges associated to NIBs, for example, these do not hold as much energy as LIBs due to the larger ionic size and weight and higher redox potential of Na compared to Li. Hence, the development of anode and cathode materials capable to deliver stable high specific capacities is crucial in achieving NIBs with comparable energy density to LIBs.
In the area of anode materials for NIBs, we are currently investigating hard-carbon-based and titanate materials. Our group is currently developing cost-effective production methods of these materials as well as investigating in-depth the structural and dynamic processes occurring during battery cycling. These studies will allow us to provide a rational materials design to mitigate long-term degradation. Additionally, despite several promising materials being proposed and tested in our lab, the interaction of the conventional electrolytes with electrodes and SEI formation is still poorly understood and known to impact negatively the performance of NIBs. In this matter, our group is currently involved in this field of research in collaboration with NEXGENNA partners to build up effective electrolytes that are stable with our electrode materials.
On the other hand, the development of stable high voltage and high capacity cathodes is desired to obtain NIBs with high-energy density. For that, our lab is researching on the stabilization of high energy density layered oxides based on low-cost abundant elements (e.g. Fe, Cu or Mn). We also aim to understand questions regarding the sodium storage mechanism and the structure-function correlation in these materials, which remain still unanswered for most of them.
Beyond Li-ion batteries: Magnesium batteries
Rechargeable magnesium batteries (RMBs) have arisen as promising substitutes to LIBs due to the divalent nature, high abundance, low-cost, and environmental benignity of magnesium. To enable high-energy densities in RMBs, it is crucial the use of Mg metal as anode, which exhibits a large volumetric capacity of 3882 mAh/cm3 (vs. 2044 mAh/cm3 for Li) and a redox potential of EMg2+/Mg= −2.36 V vs. SHE. Moreover, Mg is less prone to dendrite formation upon plating/stripping at realistic current densities. Additionally, air exposure is much less of a safety issue with magnesium than it is with lithium since the former does not usually form toxic and/or dangerous compounds, leading to more cost-effective and eco-friendly industrial processes. Currently, there are key challenges associated to the implementation of RMBs, which reside in the realisation of Mg-based electrolytes stable over a wide voltage window, compatible with Mg and non-corrosive to cell components, and the development of suitable high-energy density cathode materials.
Our group is developing novel spinel-based cathode materials for RMBs, which we are studying in combination with anodes and electrolyte systems for optimal electrochemical performance. Our main goals are: 1) to improve the stability and kinetics of Mg intercalation in these materials by altering the (micro)structure of these materials and 2) to unravel the degradation mechanisms occurring upon cycling that lead to a fast capacity fading to inform our synthetic strategies.
Rechargeable aqueous Zn-ion batteries
Rechargeable aqueous zinc-ion batteries (AZIBs) have recently attracted a lot of attention owing to the natural abundance, non-toxicity, safety and cost-effectiveness of zinc. In addition to this, high theoretical capacity (820 mAh/g), low redox potential (-0.76 V vs. SHE), and the stability of the zinc metal in aqueous electrolytes make this battery technology a promising alternative to state-of-the-art rechargeable batteries to be used in smart grid energy storage. The success of this technology remains a challenge as AZIBs require high demanding conditions, for example, finding multivalent electrode materials that can provide a large interlayer space for ionic intercalation.
We are developing novel and stable electrode materials for AZIBs and exploring their performance when combining these with different aqueous electrolyte formulations. We employ a combination of techniques such as powder X-ray diffraction, X-ray absorption near-edge spectroscopy, Fourier-transform infrared spectroscopy and Inductively coupled plasma-optical emission spectrometry to provide insight into the complex charge-compensation mechanisms occurring in these materials, where reactions beyond Zn-ion (de)insertion take place due to the crucial role of water in these systems.