Structural characterization of porous carbon materials is critical for the evaluation of their synthesis procedures and performance as electrodes in alkali-ion batteries. Throughout the last decades, many methods have been employed to determine porosity properties from gas adsorption such as surface area, pore size distribution (PSD) and real density. However, gas adsorption models use 1D structures of carbon nanopores, although adsorption and separation properties of nanoporous carbons are governed by 3D pore parameters. Estimating the 3D nanostructure of nanoporous carbons using gas adsorption would accelerate progress in fundamental research and optimisation of nanoporous carbon electrodes. We report here a promising 3D pore nanostructural characterization from gas adsorption. Using atomistic simulations, we have generated a database of large and realistic 3D porous carbon structures spanning a wide range of pore sizes and geometries. The 3D pore structures correlate very well with the local carbon structure as experimentally determined by high-resolution TEM observations and can successfully predict adsorption of different gases. This is a powerful procedure that can be extended to other materials, and with enough computer power, to larger pore sizes. Such advanced characterisation techniques able to give insight into the pore structure will enable to understand the role of porosity and pore topology in ion storage. 

UK is dedicated to achieving net-zero emissions by 2050, aiming for a delicate balance
between greenhouse gas emissions and their removal from the atmosphere. To accomplish
this ambitious goal, UK is actively exploring renewable energy. Scotland has emerged as a
frontrunner in renewable energy, particularly in wind power;1 however, given the intermittent
nature of energy resources like wind, reliable, clean energy storage solutions are imperative.
In this context, devices such as supercapacitors and batteries play pivotal roles in ensuring
energy stability and sustainability.
While lithium-ion (Li-ion) batteries are currently dominant in the global market,
concerns over the scarcity of lithium highlight the need for sustainable alternatives.2 The
development of nonaqueous multivalent ion batteries, such as those utilizing magnesium
(Mg), presents a promising avenue to build upon the benefits of dendrite- free metal plating-
stripping (safety), high abundance, and higher volumetric energy density, surpassing the
limitations associated with Li-ion technology. Yet, the challenge lies in identifying fast Mg2+ ion
conducting materials to achieve satisfactory energy, particularly power density. Directly
translating state-of-the-art positive electrode materials for Li-ion systems renders adversities
within the Mg2+ system. Nevertheless, with ongoing advancements in Mg electrolytes and
cathode materials, significant progress has been achieved.3
My talk will delve into various material chemistries, including chalcogenides, oxides,
and polyanions, assessing the merits and challenges of each as Mg ion cathode.4, 5
Furthermore, the development of new materials should be synchronized with the
advancement of techniques for analyzing battery components, especially during the cycling
process. Consequently, I will also discuss recent findings aimed at improving Mg2+ diffusion
by adjusting their interactions with cathode hosts, offering insights into the future direction of
research in this dynamic field.

Lithium-ion battery (LIB) technology, introduced in the 1990s, delivers significant performance enhancements and increased energy density, becoming the dominant choice for energy storage in portable devices, electric vehicles, and smart grids. LIBs incorporate carbon anode materials and lithium-transition metal oxide-based cathode materials to achieve high specific capacities, raising the energy density of secondary batteries to 400 Wh/L, making them well-suited for high-power applications such as power tools and hybrid vehicles[1], [2]. However, electrode degradation and stability during extended cycling at high currents remain areas that require improvement[3]. Improving electrode materials to achieve structural stability by mitigating side reactions is critical. Applying thin film coatings on electrode surfaces, in the form of a thin shell, has shown to be an effective strategy for overcoming performance limitations[4], [5], [6]. Atomic/molecular layer deposition (ALD/MLD) offers a promising approach by creating an optimal interface between the electrode surface and the electrolyte[7], [8], as some of us have already demonstrated for silicon anode [9]. In this study, we present the controlled growth and influence of thin alucone (AlGL) films on graphite anode and NMC622 cathode surfaces using the MLD technique to enhance capacity and reduce degradation in lithium-ion batteries. The discharge specific capacity of graphite anode material increased to 168 mAh/g with the alucone thin film from 80 mAh/g at 0.5C. This coating strategy also stabilizes the formation of the SEI film, improves Coulombic efficiency (CE), and enhances long-term cycling stability by reducing capacity loss.

Aluminium metal batteries are a compelling post-lithium technology to diversify the battery market. In addition to its high theoretical capacity, aluminium is the most abundant metal in the earth’s crust and its processing is well established, leading to low cost and promising recyclability. Aluminium graphite dual-ion batteries (AGDIBs) were first developed in 2015 and have since gained attention for their affordable graphite electrodes, non-flammable ionic liquid electrolytes, and high power density. The AGDIB utilises an aluminium chloride room-temperature ionic liquid to allow de-/intercalation of AlCl₄^- anions into the graphitic carbon cathode and electrodeposition/stripping of aluminium from Al₂C₇^- anions at the metallic aluminium anode. However, a significant challenge to this configuration is limited understanding of the stability of cell components in the corrosive electrolyte. Particularly little is known about the fundamental processes of corrosion and interphase formation at the anode-electrolyte interface and their effects on aluminium electrodeposition.  

Building on promising studies of graphite cathode and chloroaluminate electrolyte materials, this work aims to further fundamental understanding of the device by in situ and ex situ studies of the anode surface during battery operation. 2-electrode full cell configurations were galvanostatically cycled to different potentials and disassembled anodes were washed in dimethyl carbonate for ex situ analysis. A systematic study of the anode morphology by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and atomic force microscopy (AFM) revealed the growth of concentric ring features as a result of side-reactions causing heterogeneous corrosion and electrodeposition. Solid electrolyte interphase formation on these porous features was then studied using X-ray photoelectron spectroscopy (XPS) and cross-sectional transmission electron microscopy (TEM) to reveal significant insertion of chlorine and some incorporation of iron species into the existing native oxide layer. This phenomenon was further studied by operando Near Edge X-ray Absorption Fine Structure spectroscopy (NEXAFS) in a custom cell to achieve realistic testing conditions.

This work shows that the anode-electrolyte interface is more complex than often assumed, with heterogeneous deposition impacting cell stability, as well as solid electrolyte interphase formation affecting diffusion for deposition and corrosion. Better understanding of these phenomena is key for targeted modifications of the system to improve the electrolyte and protect the anode surface to enable longer shelf and cycle life of aluminium batteries.

The demand for extended-range electric vehicles has created a renaissance of interest in replacing the common metal-ion with higher energy-density metal-anode batteries, i.e. lithium, sodium and zinc. However, metal cells suffer from capacity fading and potential safety issues due to uneven metal electrodeposition.

"Anode-free" (AF) batteries comprise a metal-ion cathode and a current collector, the cathode consisting of the metal source. The metal is then plated on the current collector during charging. These batteries present a significant advantage due to their higher energy density, superior safety, and ease of production. However, realising metal and AF batteries requires a better understanding of alkali and multivalent metal plating, short-circuiting mechanisms, and metal battery degradation.

A considerable performance gap between lithium symmetric cells and practical lithium batteries motivated us to explore the correlation between the shape of voltage traces and degradation. The coupling of operando nuclear magnetic resonance (NMR) and galvanostatic electrochemical impedance spectroscopy (GEIS) allowed us to observe metal batteries' electrochemical and chemical dynamics and degradation in real-time without affecting the electrochemical reactions in the cell. 

"Soft shorts" are small localised electrical connections between two electrodes that allow the co-existence of direct electron transfer and interfacial reaction. Although soft shorts were identified as a potential safety issue for lithium-ion batteries in the early nineties, their detection and prevention were not widely studied. Using coupled EIS and operando NMR, we showed that transient (i.e., soft) shorts form in realistic conditions for battery cycling.

The typical rectangular-shaped voltage trace, widely considered ideal, was proven, under the conditions studied here, to be a result of soft shorts. Recoverable soft-shorted cells were demonstrated during a symmetric cell polarisation experiment, defining a new type of critical current density: the current density at which the soft shorts are not reversible. We showed that soft shorts are predictive towards the formation of hard shorts, demonstrating the potential use of EIS as a relatively low-cost and non-destructive method for early detection of catastrophic shorts and battery failure while demonstrating the strength of operando NMR as a research tool for metal plating in metal batteries. 

While today's lithium-ion battery chemistries are ubiquitous, powering mobile devices and increasingly electric vehicles, they contain critical minerals such as cobalt and minerals with supply concerns, mainly if these batteries are used at the scale needed to meet the 2050 climate goals. To address this challenge, "beyond-lithium" technologies are investigated. These battery chemistries allow earth-abundant, safer, and low-cost energy storage.

Sodium metal anodes have been studied broadly, assuming sodium and lithium metal anodes respond similarly to cycling. We established that lithium and sodium short circuit formation mechanisms fundamentally differ and strongly depend on electrolyte composition and SEI stability.

Zinc metal anodes have gained increasing interest due to the sustainability of the aqueous electrolytes; however, a greater insight into their unique plating, hydrogen evolution, and corrosion mechanisms is critical. In our SECM study of zinc plating, we compared the effects of various electrolyte compositions and plating conditions on SEI heterogeneity and zinc metal morphology. We showed that the heterogeneity of the surface reactions on zinc electrodes has a more significant effect on zinc anode cyclability than electrolyte stability.

This new understanding of the metal plating mechanism is crucial to developing the next generation of rechargeable batteries with high energy density, prolonged cycling life and improved sustainability. A fundamental understanding and reliable testing methods for soft short circuits are critical for commercialising metal (e.g., metal-air, metal-sulphur) and AF batteries.

The lithium-oxygen (Li-O₂) battery, with its extremely high theoretical energy density (> 3500 Wh/kg), is considered one of the most promising candidates for next-generation energy storage.[1] However, it suffers from serious side reactions due to the instability of both the carbon cathode and the electrolytes to reactive intermediates such as lithium superoxide (LiO₂), singlet oxygen (¹O₂), and even the discharge product lithium peroxide (Li₂O₂) formed during ORR/OER processes.[2] In addition, neither carbon cathodes nor electrolytes can withstand a high overpotential and decompose under the operating conditions of a Li-O₂ battery.[3] To deepen the fundamental understanding of the failure mechanisms in Li-O₂ batteries, it is crucial to decouple the side reactions of the cathode and electrolyte.

As reported in our previous work, topological-defect-rich graphene mesosponge (GMS) synthesized by chemical vapor deposition (CVD) using Al₂O₃ as a template is a promising carbon cathode for Li-O₂ batteries, exhibiting a large capacity.[4] Moreover, the large surface area of GMS makes it a good substrate for solid catalyst loading.[5] In this work, isotope ¹³C-GMS was first synthesized using high-purity ¹³C-CH₄ as a carbon source for CVD. Then, we unraveled the critical influence of overpotential in Li-O₂ batteries by using ¹³C-GMS cathodes with hexagonal close-packed (hcp) and face center cubic (fcc) Ru crystals as catalysts. Under the monitoring of in situ differential electrochemical mass spectrometry (DEMS), side reactions caused by isotopic labeling of ¹³C-based cathodes and conventional ¹²C-based electrolytes were first decoupled. Our result shows that the lower overpotential of fcc-Ru compared to hcp-Ru only inhibits carbon cathode degradation but accelerates electrolyte degradation, which severely limits the cycling performance of Li-O₂ batteries, especially when a limited amount of electrolyte was used. Eventually, the cyclability of Li-O₂ batteries can be described as the liquid in a barrel. With sufficient Li anode, cyclability is determined by the shortest rod of cathode stability or electrolyte stability. We would like to draw attention to the critical evaluation of side reactions in Li-O₂ batteries. And our ¹³C-GMS can also be useful to decouple the side reaction in other batteries.

Sodium ion batteries (SIBs) are a potential alternative to diversify the energy landscape, beyond Lithium-ion batteries (LIBs), due to their similar storage mechanism and easy technology transfer. Currently, the benchmark anodes for SIBs are hard carbons (HCs), since sodium ions do not intercalate into graphite. HCs can be produced from a variety of waste precursors and therefore are more sustainable and less geopolitically compromised than natural graphite, mainly concentrated in China. The electrochemical degradation of SIBs can be attributed to the greater reactivity of HC anodes compared to graphite. A deeper operando understanding of the degradation mechanisms in SIBs, coupled with engineering of the materials and electrolyte to ensure that a better and more protective solid electrolyte interface (SEI) is formed, is needed for an accelerated scale up of this technology. In this talk I will show you some of the strategies we have developed for these aims.

Amorphous silicon nitride (a-Si₃N₄) has emerged as a promising anode material for lithium-ion batteries due to its high theoretical capacity and improved stability compared to pure silicon anodes. However, the atomic-scale mechanisms of lithium (Li) incorporation and storage in a-Si₃N₄ remain elusive. In this work we employ first-principles calculations to investigate the initial stages of lithiation in a-Si₃N₄, to understand the various modes of Li incorporation that drive the transition from irreversible matrix formation to reversible Li storage. Our research identifies three distinct modes of Li incorporation, each associated with different local structural environments and Li concentrations. Notably, we uncover the crucial role intrinsic charge trapping plays in both the irreversible and reversible Li incorporation, firstly, driving the matrix formation and secondly, facilitating reversible Li storage and charge transport. These insights allow strategies for the optimisation of a-Si₃N₄-based anodes to be devised, with the potential to tune the balance between matrix formation and productive Li storage. These insights provide a fundamental understanding of the lithiation process in a-Si₃N₄ and pave the way for the design of next-generation anode materials with enhanced performance.

Major advances in high energy density lithium-ion batteries require new compositions and underpinning materials science. Indeed, a greater fundamental understanding into battery materials require atomic- and nano-scale characterisation of their ion transport, electronic and local structural behavior, which are important for optimizing performance. In this context, combined modelling-experimental work has been a powerful approach for investigating these properties. This presentation will describe such studies [1, 2] in two principal areas: (i) investigating redox processes and nanostructures of Li-rich layered oxide and disordered rocksalt oxyfluoride compounds as promising high capacity battery cathodes; here, the atomic-scale mechanisms governing oxygen redox behaviour in Li-rich structures are not fully understood (ii) ion transport and doping mechanisms in solid electrolytes for solid-state batteries including oxide and thiophosphate-type fast-ion conductors.

[1] K. McColl, M.S. Islam et al., Nature Mater., 23, 826 (2024); K. McColl et al., Nature Comms, 13, 5275 (2022).

[2] J.A. Dawson and M.S. Islam., ACS Mater. Lett., 4, 424 (2022); A.D. Poletayev et al., Nature, 625, 7996 (2024).

During the past decades, the development of alternative energy sources has become increasingly important as the growing consumption of non-regenerative fossil energy poses a threat to the environment. Hence, the development of batteries with performance beyond the intrinsic limits of lithium-ion batteries plays an important role. Especially lithium metal anodes show highest volumetric and gravimetric energy density of all anode materials, however, suffering from safety issues and capacity fading due to uncontrolled electrodeposition.[1] One major issue is short circuits, which refer to small local electrical contacts between the electrodes. These contacts are limiting the performance of the battery and can lead to hazardous situations. Although lithium plating has been studied widely, a better understanding of the short-circuiting mechanisms and metal battery failure is required

The Li//Li symmetric cell is one basic configuration to study the degradation mechanism correlated with electrodeposition and interface layers. The cycling time of Li symmetric cells has been regarded as a key metric indicating the metal anodes’ lifespan. However, there is a considerable performance gap between symmetric and realistic lithium metal cells. Developing a reliable testing procedure for lithium metal cells is critical for realising the emerging “anode-free’’ and “beyond lithium-ion” batteries, like Li-S and Li-O₂ batteries.

Therefore, the involved local structural changes that correlate with the electrochemical processes need to be unveiled during the operation of lithium metal batteries, suitably by in situ methods. We coupled in situ impedance spectroscopy and operando NMR for the first time to detect that transient “soft”-short circuits are formed under realistic cycling conditions. Especially this degradation mechanism is typically overseen as their electrochemical signatures are often not distinct.[2]

The detection of reversible soft shorts during a symmetrical cell polarization experiment suggests that the critical current density should be redefined to reflect the current density at which the degradation is not recoverable anymore. Furthermore, we showed that medium-frequency GEIS, as a readily available and low-cost technique, could be used to predict upcoming catastrophic battery failures. [3] Hence, this work will potentially contribute to the development of low-cost state-of-health battery analysis that has the potential to be implemented in electric vehicles and mobile electronics. If implemented, the customers will benefit from safer and higher-energy batteries.

Therefore, in situ NMR and impedance spectroscopy are a powerful and non-destructive method combinations to investigate a key problem that leads to the degradation of lithium metal batteries and potential safety issues. This understanding is crucial to improve the safety of next-generation batteries and enables faster commercialization of, e.g., Li-S, anode-free (lithium and sodium) and solid-state batteries.

The difficulty in characterizing the complex structures of nanoporous carbon electrodes has led to a lack of clear design principles with which to improve supercapacitor energy storage devices. While pore size has long been considered the main lever to improve capacitance, our study of a large series of commercial nanoporous carbons finds a lack of correlation between pore size and capacitance.[1] Instead nuclear magnetic resonance spectroscopy measurements and simulations reveal a strong correlation between structural disorder in the electrodes and capacitance.[1] More disordered carbons with smaller graphene-like domains show higher capacitances due to the more efficient storage of ions in their nanopores. Furthermore, our recent Raman spectroscopy experiments provide additional support for disorder-driven capacitance.[2] Specifically carbons with smaller ID/IG ratios have smaller-graphene like domains and larger capacitance values. Our findings will stimulate a new wave of research to understand and exploit disorder to achieve highly energy dense supercapacitors.

The global policy push towards Net Zero and the decarbonisation of the energy and transport sectors will lead to a surge in lithium-ion battery (LIB) demand for grid storage applications and electric vehicles. Naturally, this in turn will result in growing amounts of LIB waste in the coming decades raising concerns about appropriate waste treatment solutions. Disposing of LIBs in landfills can lead to environmental and safety risks, where toxic chemicals could leach into the environment or landfill fires can be caused by defect battery cells. Moreover, valuable critical materials such as lithium and cobalt, which suffer from growing supply chain risks, would be simply thrown away. Responsible end-of-life LIB waste management is therefore increasingly becoming the focus of the academic community and policy makers alike. Here, the ideal scenario would be a circular battery economy, where LIB waste is being recycled and the recovered materials are fed back into the battery manufacturing process. This could further alleviate supply chain pressures and counter-balance negative environmental impacts incurred from mining activities, which will need to significantly expand in the future to match the increasing battery materials demand.

Whilst the importance of battery recycling cannot be negated, the recycling industry is still facing significant challenges such as complicated battery disassembly procedures and the establishment of efficient recycling processes. These obstacles are often associated with financial burdens and risks slowing down the growth of the recycling industry.

In this talk, I will provide an overview of the techno-economics of LIB recycling from disassembly to materials recovery and will highlight some of the main challenges we need to solve to establish a truly sustainable and financially viable circular economy for LIBs.