Showing papers by "University of Wollongong published in 2021"

Electroceramics for High-Energy Density Capacitors: Current Status and Future Perspectives

Abstract: Materials exhibiting high energy/power density are currently needed to meet the growing demand of portable electronics, electric vehicles and large-scale energy storage devices. The highest energy densities are achieved for fuel cells, batteries, and supercapacitors, but conventional dielectric capacitors are receiving increased attention for pulsed power applications due to their high power density and their fast charge-discharge speed. The key to high energy density in dielectric capacitors is a large maximum but small remanent (zero in the case of linear dielectrics) polarization and a high electric breakdown strength. Polymer dielectric capacitors offer high power/energy density for applications at room temperature, but above 100 °C they are unreliable and suffer from dielectric breakdown. For high-temperature applications, therefore, dielectric ceramics are the only feasible alternative. Lead-based ceramics such as La-doped lead zirconate titanate exhibit good energy storage properties, but their toxicity raises concern over their use in consumer applications, where capacitors are exclusively lead free. Lead-free compositions with superior power density are thus required. In this paper, we introduce the fundamental principles of energy storage in dielectrics. We discuss key factors to improve energy storage properties such as the control of local structure, phase assemblage, dielectric layer thickness, microstructure, conductivity, and electrical homogeneity through the choice of base systems, dopants, and alloying additions, followed by a comprehensive review of the state-of-the-art. Finally, we comment on the future requirements for new materials in high power/energy density capacitor applications.

Boosting Zinc Electrode Reversibility in Aqueous Electrolytes by Using Low-Cost Antisolvents

Abstract: Antisolvent addition has been widely studied in crystallization in the pharmaceutical industries by breaking the solvation balance of the original solution. Here we report a similar antisolvent strategy to boost Zn reversibility via regulation of the electrolyte on a molecular level. By adding for example methanol into ZnSO4 electrolyte, the free water and coordinated water in Zn2+ solvation sheath gradually interact with the antisolvent, which minimizes water activity and weakens Zn2+ solvation. Concomitantly, dendrite-free Zn deposition occurs via change in the deposition orientation, as evidenced by in situ optical microscopy. Zn reversibility is significantly boosted in antisolvent electrolyte of 50 % methanol by volume (Anti-M-50 %) even under harsh environments of -20 °C and 60 °C. Additionally, the suppressed side reactions and dendrite-free Zn plating/stripping in Anti-M-50 % electrolyte significantly enhance performance of Zn/polyaniline coin and pouch cells. We demonstrate this low-cost strategy can be readily generalized to other solvents, indicating its practical universality. Results will be of immediate interest and benefit to a range of researchers in electrochemistry and energy storage.

Five-Year Outcomes With Pembrolizumab Versus Chemotherapy for Metastatic Non-Small-Cell Lung Cancer With PD-L1 Tumor Proportion Score >= 50%

Abstract: PURPOSEWe report the first 5-year follow-up of any first-line phase III immunotherapy trial for non–small-cell lung cancer (NSCLC). KEYNOTE-024 (ClinicalTrials.gov identifier: NCT02142738) is an op...

Electrolyte Design for In Situ Construction of Highly Zn 2+ -Conductive Solid Electrolyte Interphase to Enable High-Performance Aqueous Zn-Ion Batteries under Practical Conditions.

Abstract: Rechargeable aqueous Zn-ion batteries promise high capacity, low cost, high safety, and sustainability for large-scale energy storage The Zn metal anode, however, suffers from the dendrite growth and side reactions that are mainly due to the absence of an appropriate solid electrolyte interphase (SEI) layer Herein, the in situ formation of a dense, stable, and highly Zn2+ -conductive SEI layer (hopeite) in aqueous Zn chemistry is demonstrated, by introducing Zn(H2 PO4 )2 salt into the electrolyte The hopeite SEI (≈140 nm thickness) enables uniform and rapid Zn-ion transport kinetics for dendrite-free Zn deposition, and restrains the side reactions via isolating active Zn from the bulk electrolyte Under practical testing conditions with an ultrathin Zn anode (10 µm), a low negative/positive capacity ratio (≈23), and a lean electrolyte (9 µL mAh-1 ), the Zn/V2 O5 full cell retains 944% of its original capacity after 500 cycles This work provides a simple yet practical solution to high-performance aqueous battery technology via building in situ SEI layers

Recent Progress on the Alloy-Based Anode for Sodium-Ion Batteries and Potassium-Ion Batteries.

Abstract: High-energy batteries with low cost are urgently needed in the field of large-scale energy storage, such as grid systems and renewable energy sources. Sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) with alloy-based anodes provide huge potential due to their earth abundance, high capacity, and suitable working potential, and are recognized as attractive alternatives for next-generation batteries system. Although some important breakthroughs have been reported, more significant improvements are still required for long lifetime and high energy density. Herein, the latest progress for alloy-based anodes for SIBs and PIBs is summarized, mainly including Sn, Sb, Ge, Bi, Si, P, and their oxides, sulfides, selenides, and phosphides. Specifically, the material designs for the desired Na+ /K+ storage performance, phase transform, ionic/electronic transport kinetics, and specific chemical interactions are discussed. Typical structural features and research strategies of alloy-based anodes, which are used to facilitate processes in battery development for SIBs and PIBs, are also summarized. The perspective of future research of SIBs and PIBs is outlined.

Multifunctional applications of biochar beyond carbon storage

Abstract: Biochar is produced as a charred material with high surface area and abundant functional groups by pyrolysis, which refers to the process of thermochemical decomposition of organic material at elev...

Hard carbon anodes: fundamental understanding and commercial perspectives for Na-ion batteries beyond Li-ion and K-ion counterparts

Abstract: Hard carbon (HC) is recognized as a promising anode material with outstanding electrochemical performance for alkali metal-ion batteries including lithium-ion batteries (LIBs), as well as their analogs sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). Herein, a comprehensive review of the recent research is presented to interpret the challenges and opportunities for the applications of HC anodes. The ion storage mechanisms, materials design, and electrolyte optimizations for alkali metal-ion batteries are illustrated in-depth. HC is particularly promising as an anode material for SIBs. The solid-electrolyte interphase, initial Coulombic efficiency, safety concerns, and all-climate performances, which are vital for practical applications, are comprehensively discussed. Furthermore, commercial prototypes of SIBs based on HC anodes are extensively elaborated. The remaining challenges and research perspectives are provided, aiming to shed light on future research and early commercialization of HC-based SIBs.

Regulation methods for the Zn/electrolyte interphase and the effectiveness evaluation in aqueous Zn-ion batteries

Abstract: Aqueous Zn-ion batteries (ZIBs) have inspired an overwhelming number of literature studies due to their safety, cost effectiveness, and environmental benignity. Directly employing metallic Zn foil as an anode significantly simplifies battery manufacturing and simultaneously broadens the operating voltage window of aqueous batteries, benefiting from its high overpotential against electrolyte decomposition. Nevertheless, serious issues, such as dendrite growth and side reactions, occurring at the Zn/electrolyte interphase, make the Coulombic efficiency and lifespan of Zn metal electrodes far from satisfactory, which has also been motivating new research interest in interfacial engineering to solve these problems. Owing to the rapid evolution of this new area, it is highly desirable to provide current and timely updates of interfacial strategies and their effectiveness evaluation. From the two sides – the electrode and the electrolyte at the interphase – this review thoroughly summarizes our fundamental understanding of interfacial strategies, including designing mechanisms, creating new methods, and technical challenges. Importantly, this review also analyses the effectiveness evaluation techniques for interfacial strategies, including electrochemical methods, characterization measurements, and computational simulations, providing guidelines for the accurate evaluation and analysis of ZIBs in the future.

High-strength scalable MXene films through bridging-induced densification

Abstract: MXenes are a growing family of two-dimensional transition metal carbides and/or nitrides that are densely stacked into macroscopically layered films and have been considered for applications such a...

Forest microclimates and climate change: Importance, drivers and future research agenda.

Abstract: Forest microclimates contrast strongly with the climate outside forests. To fully understand and better predict how forests' biodiversity and functions relate to climate and climate change, microclimates need to be integrated into ecological research. Despite the potentially broad impact of microclimates on the response of forest ecosystems to global change, our understanding of how microclimates within and below tree canopies modulate biotic responses to global change at the species, community and ecosystem level is still limited. Here, we review how spatial and temporal variation in forest microclimates result from an interplay of forest features, local water balance, topography and landscape composition. We first stress and exemplify the importance of considering forest microclimates to understand variation in biodiversity and ecosystem functions across forest landscapes. Next, we explain how macroclimate warming (of the free atmosphere) can affect microclimates, and vice versa, via interactions with land-use changes across different biomes. Finally, we perform a priority ranking of future research avenues at the interface of microclimate ecology and global change biology, with a specific focus on three key themes: (1) disentangling the abiotic and biotic drivers and feedbacks of forest microclimates; (2) global and regional mapping and predictions of forest microclimates; and (3) the impacts of microclimate on forest biodiversity and ecosystem functioning in the face of climate change. The availability of microclimatic data will significantly increase in the coming decades, characterizing climate variability at unprecedented spatial and temporal scales relevant to biological processes in forests. This will revolutionize our understanding of the dynamics, drivers and implications of forest microclimates on biodiversity and ecological functions, and the impacts of global changes. In order to support the sustainable use of forests and to secure their biodiversity and ecosystem services for future generations, microclimates cannot be ignored.

Bio-inspired design of an in situ multifunctional polymeric solid–electrolyte interphase for Zn metal anode cycling at 30 mA cm−2 and 30 mA h cm−2

Abstract: A solid–electrolyte interphase (SEI) is highly desirable to restrain Zn dendrite growth and side reactions between a Zn anode and water in rechargeable aqueous zinc-ion batteries (RAZBs), but remains a challenge. Here, inspired by the bio-adhesion principle, a stable SEI of polydopamine is constructed successfully on a Zn anode via an in situ electrochemical polymerization process of a dopamine additive. This in situ polymeric SEI offers multifunctional features with abundant functional groups and outstanding hydrophilicity for regulating Zn nucleation to achieve dendrite-free Zn deposition, high Zn-ion conductivity for fast Zn2+ transport, and strong adhesion capability for blocking interfacial side reactions. Consequently, the Zn electrodes exhibited high reversibility with 99.5% coulombic efficiency and outstanding stability, even at ultrahigh current density and areal capacity (30 mA cm−2 and 30 mA h cm−2). Moreover, a prolonged lifespan can be attained for the Zn/V2O5 full cell in a lean electrolyte (9 μL mA h−1) and with a low capacity ratio of the negative electrode to the positive electrode (∼2). This work provides inspiration for the design of SEI layers in aqueous battery chemistry and promotes the practical application of RAZBs.

Battery energy-storage system: A review of technologies, optimization objectives, constraints, approaches, and outstanding issues

Abstract: Due to urbanization and the rapid growth of population, carbon emission is increasing, which leads to climate change and global warming. With an increased level of fossil fuel burning and scarcity of fossil fuel, the power industry is moving to alternative energy resources such as photovoltaic power (PV), wind power (WP), and battery energy-storage systems (BESS), among others. BESS has some advantages over conventional energy sources, which include fast and steady response, adaptability, controllability, environmental friendliness, and geographical independence, and it is considered as a potential solution to the global warming problem. This paper provides a comprehensive review of the battery energy-storage system concerning optimal sizing objectives, the system constraint, various optimization models, and approaches along with their advantages and weakness. Furthermore, for better understanding, the optimization objectives and methods have been classified into different categories. This paper also provides a detailed discussion on the BESS applications and explores the shortages of existing optimal BESS sizing algorithms to identify the gaps for future research. The issues and challenges are also highlighted to provide a clear idea to the researchers in the field of BESS. Overall, this paper conveys some significant recommendations that would be useful to the researchers and policymakers to structure a productive, powerful, efficient, and robust battery energy-storage system toward a future with a sustainable environment.

Sodium transition metal oxides: the preferred cathode choice for future sodium-ion batteries?

Abstract: The exploration of next-generation sodium-ion batteries (SIBs) is a worldwide concern to replace the current commercial lithium-ion batteries, mitigating the increasing exhaustion of Li resources. Sodium transition metal oxides are considered to be one of the most promising cathode materials for SIBs. The anionic redox reaction in Li-rich transition metal oxides is capable of providing extra capacity in addition to the cationic redox activities in lithium-ion batteries. A similar phenomenon exists in SIBs, which even applies to Na-deficient transition metal oxides. Moreover, transition metal oxides with mixed phase also demonstrate great potential. In this review, studies on anionic redox are first systematically introduced. The up-to-date advances on high-capacity transition metal oxide cathode materials for SIBs are then classified and summarized in different groups associated with or without anionic redox. The existing challenges as well as available solutions and strategies are discussed, and proposals with new insights are made at the end. It is expected that this work can provide new perspectives on controlling the anionic redox activity and finding novel high-capacity oxide cathode materials for SIBs.

Non-carbon-supported single-atom site catalysts for electrocatalysis

Abstract: Single-atom site catalysts (SACs) have received considerable attention for electrocatalytic applications, owing to their maximum atom-utilization efficiency, well-identified active centers, and tunable supports. Carbon-supported SACs have been widely applied in electrocatalysis, and their progress has been intensively reviewed. Non-carbon-supported SACs have drawn ever-increasing attention recently, and are emerging as an indispensable class of SACs. This review comprehensively summarizes the recent exciting progress on the non-carbon-supported SACs and their applications in electrocatalytic reactions. Eight types of non-carbon-supported SACs are firstly categorized to show their diversity. Subsequently, the anchoring and stabilization mechanisms for each type of non-carbon-supported SACs are systematically unraveled. Furthermore, the advanced characterization techniques for identifying and monitoring the atomic structure of SACs are highlighted. Thereafter, the advances of non-carbon-supported SACs for electrochemical energy conversion are discussed, which emphasizes their applications in the hydrogen evolution reaction, the oxygen evolution reaction, the oxygen reduction reaction, the N2 reduction reaction, and the CO2 reduction reaction. Finally, perspective insights into the current challenges and the future prospects for non-carbon-supported SACs are provided.

Prelithiation: A Crucial Strategy for Boosting the Practical Application of Next-Generation Lithium Ion Battery.

Abstract: With the urgent market demand for high-energy-density batteries, the alloy-type or conversion-type anodes with high specific capacity have gained increasing attention to replace current low-specific-capacity graphite-based anodes. However, alloy-type and conversion-type anodes have large initial irreversible capacity compared with graphite-based anodes, which consume most of the Li+ in the corresponding cathode and severely reduces the energy density of full cells. Therefore, for the practical application of these high-capacity anodes, it is urgent to develop a commercially available prelithiation technique to compensate for their large initial irreversible capacity. At present, various prelithiation methods for compensating the initial irreversible capacity of the anode have been reported, but due to their respective shortcomings, large-scale commercial applications have not yet been achieved. In this review, we have systematically summarized and analyzed the advantages and challenges of various prelithiation methods, providing enlightenment for the further development of each prelithiation strategy toward commercialization and thus facilitating the practical application of high-specific-capacity anodes in the next-generation high-energy-density lithium-ion batteries.

Manipulating the Solvation Structure of Nonflammable Electrolyte and Interface to Enable Unprecedented Stability of Graphite Anodes beyond 2 Years for Safe Potassium-Ion Batteries.

Abstract: Potassium-ion batteries (PIBs) are attractive for low-cost and large-scale energy storage applications, in which graphite is one of the most promising anodes. However, the large size and the high activity of K+ ions and the highly catalytic surface of graphite largely prevent the development of safe and compatible electrolytes. Here, a nonflammable, moderate-concentration electrolyte is reported that is highly compatible with graphite anodes and that consists of fire-retardant trimethyl phosphate (TMP) and potassium bis(fluorosulfonyl)imide (KFSI) in a salt/solvent molar ratio of 3:8. It shows unprecedented stability, as evidenced by its 74% capacity retention over 24 months of cycling (over 2000 cycles) at the 0.2 C current rate. Electrolyte structure and surface analyses show that this excellent cycling stability is due to the nearly 100% solvation of TMP molecules with K+ cations and the formation of FSI- -derived F-rich solid electrolyte interphase (SEI), which effectively suppresses the decomposition of the solvent molecules toward the graphite anode. Furthermore, excellent performance on high-mass loaded graphite electrodes and in a full cell with perylenetetracarboxylic dianhydride cathode is demonstrated. This study highlights the importance of the compatibility of both electrolyte and the interface, and offers new opportunities to design the electrolyte-SEI nexus for safe and practical PIBs.

Tuning the Selective Adsorption Site of Biomass on Co 3 O 4 by Ir Single Atoms for Electrosynthesis

Abstract: The electrosynthesis from 5-hydroxymethylfurfural (HMF) is considered a green strategy to achieve biomass-derived high-value chemicals. As the molecular structure of HMF is relatively complicated, understanding the HMF adsorption/catalysis behavior on electrocatalysts is vital for biomass-based electrosynthesis. The electrocatalysis behavior can be modulated by tuning the adsorption energy of the reactive molecules. In this work, the HMF adsorption behavior on spinel oxide, Co3 O4 is discovered. Correspondingly, the adsorption energy of HMF on Co3 O4 is successfully tuned by decorating with single-atom Ir. It is observed that compared with bare Co3 O4 , single-atom-Ir-loaded Co3 O4 (Ir-Co3 O4 ) can enhance adsorption with the CC groups of HMF. The synergetic adsorption can enhance the overall conversion of HMF on electrocatalysts. With the modulated HMF adsorption, the as-designed Ir-Co3 O4 exhibits a record performance (with an onset potential of 1.15 VRHE ) for the electrosynthesis from HMF.

Contrastive Learning based Hybrid Networks for Long-Tailed Image Classification

Abstract: Learning discriminative image representations plays a vital role in long-tailed image classification because it can ease the classifier learning in imbalanced cases. Given the promising performance contrastive learning has shown recently in representation learning, in this work, we explore effective supervised contrastive learning strategies and tailor them to learn better image representations from imbalanced data in order to boost the classification accuracy thereon. Specifically, we propose a novel hybrid network structure being composed of a supervised contrastive loss to learn image representations and a cross-entropy loss to learn classifiers, where the learning is progressively transited from feature learning to the classifier learning to embody the idea that better features make better classifiers. We explore two variants of contrastive loss for feature learning, which vary in the forms but share a common idea of pulling the samples from the same class together in the normalized embedding space and pushing the samples from different classes apart. One of them is the recently proposed supervised contrastive (SC) loss, which is designed on top of the state-of-the-art unsupervised contrastive loss by incorporating positive samples from the same class. The other is a prototypical supervised contrastive (PSC) learning strategy which addresses the intensive memory consumption in standard SC loss and thus shows more promise under limited memory budget. Extensive experiments on three long-tailed classification datasets demonstrate the advantage of the proposed contrastive learning based hybrid networks in long-tailed classification.

Blue carbon as a natural climate solution

Abstract: Blue carbon ecosystems (BCEs), including mangrove forests, seagrass meadows and tidal marshes, store carbon and provide co-benefits such as coastal protection and fisheries enhancement. Blue carbon sequestration has therefore been suggested as a natural climate solution. In this Review, we examine the potential for BCEs to act as carbon sinks and the opportunities to protect or restore ecosystems for this function. Globally, BCEs are calculated to store >30,000 Tg C across ~185 million ha, with their conservation potentially avoiding emissions of 304 (141–466) Tg carbon dioxide equivalent (CO2e) per year. Potential BCE restoration has been estimated in the range of 0.2–3.2 million ha for tidal marshes, 8.3–25.4 million ha for seagrasses and 9–13 million ha for mangroves, which could draw down an additional 841 (621–1,064) Tg CO2e per year by 2030, collectively amounting to ~3% of global emissions (based on 2019 and 2020 global annual fossil fuel emissions). Mangrove protection and/or restoration could provide the greatest carbon-related benefits, but better understanding of other BCEs is needed. BCE destruction is unlikely to stop fully, and not all losses can be restored. However, engineering and planning for coastal protection offer opportunities for protection and restoration, especially through valuing co-benefits. BCE prioritization is potentially a cost-effective and scalable natural climate solution, but there are still barriers to overcome before blue carbon project adoption will become widespread. Mangroves, tidal marshes and seagrass meadows have historically been lost or degraded, threatening their ability to store carbon and provide ecosystem services. This Review details the global potential of blue carbon ecosystem protection and restoration in climate change mitigation, through carbon sequestration and co-benefit production.

Interfacial Manipulation via In Situ Grown ZnSe Cultivator toward Highly Reversible Zn Metal Anodes.

Abstract: Zn metal anode has garnered growing scientific and industrial interest owing to its appropriate redox potential, low cost, and high safety. Nevertheless, the instability of Zn anode caused by dendrite formation, hydrogen evolution, and side reactions has greatly hampered its commercialization. Herein, an in situ grown ZnSe overlayer is crafted over one side of commercial Zn foil via chemical vapor deposition in a scalable manner, aiming to achieve optimized electrolyte/Zn interfaces with large-scale viability. Impressively, thus-derived ZnSe coating functions as a cultivator to guide oriented growth of Zn (002) plane at the infancy stage of stripping/plating cycles, thereby inhibiting the formation of Zn dendrites and the occurrence of side reactions. As a result, high cyclic stability (1530 h at 1.0 mA cm-2 /1.0 mAh cm-2 ; 172 h at 30.0 mA cm-2 /10.0 mAh cm-2 ) in symmetric cells is harvested. Meanwhile, when paired with V2 O5 based cathode, assembled full cell achieves an outstanding capacity (194.5 mAh g-1 ) and elongated lifespan (a capacity retention of 84% after 1000 cycles) at 5.0 A g-1 . The reversible Zn anode enabled by the interfacial manipulation strategy via ZnSe cultivator is anticipated to satisfy the demand of commercial use.

The 2021 battery technology roadmap

Abstract: Sun, wind and tides have huge potential in providing us electricity in an environmental-friendly way. However, its intermittency and non-dispatchability are major reasons preventing full-scale adoption of renewable energy generation. Energy storage will enable this adoption by enabling a constant and high-quality electricity supply from these systems. But which storage technology should be considered is one of important issues. Nowadays, great effort has been focused on various kinds of batteries to store energy, lithium-related batteries, sodium-related batteries, zinc-related batteries, aluminum-related batteries and so on. Some cathodes can be used for these batteries, such as sulfur, oxygen, layered compounds. In addition, the construction of these batteries can be changed into flexible, flow or solid-state types. There are many challenges in electrode materials, electrolytes and construction of these batteries and research related to the battery systems for energy storage is extremely active. With the myriad of technologies and their associated technological challenges, we were motivated to assemble this 2020 battery technology roadmap.

Spinel/Post-spinel engineering on layered oxide cathodes for sodium-ion batteries

Abstract: Sodium-ion batteries (SIBs) have attracted much scientific interest for use in large-scale energy storage systems because sodium is cheaper than lithium. However, the large radius of Na+ and barriers to Na+ transport result in sluggish kinetics and complicated structural distortion, leading to unsatisfactory rate capability and poor cycling stability. It therefore is essential to develop an electrode with enhanced kinetics and a stable structure during cycling to improve SIB performance. Among the various layered oxide cathodes, those with a spinel-like structure could play an important role in boosting electron transport because of their excellent intrinsic conductivity, including by coordinating with Na+ insertion/extraction. Moreover, thanks to the inherent high stability of the spinel-like phase, it could function as a stabilizer for host cathode structures. This review summarizes recent advances in spinel engineering on layered oxide cathodes to boost Na+ transport kinetics and provide structural stability to achieve high-performance SIBs, focusing particularly on post-spinel structures, layered oxide integrated spinel-like structures, and spinel transition. The insights proposed in this review will be useful for guiding rational structural engineering and design to drive the development of new materials and chemistries in Na-based electrode materials.

The 2019/2020 mega-fires exposed Australian ecosystems to an unprecedented extent of high-severity fire

Abstract: Extreme fire seasons characterised by very large 'mega-fires' have demonstrably increased area burnt across forested regions globally. However, the effect of extreme fire seasons on fire severity, a measure of fire impacts on ecosystems, remains unclear. Very large wildfires burnt an unprecedented area of temperate forest, woodland and shrubland across south-eastern Australia in 2019/2020, providing an opportunity to examine the impact of extreme fires on fire severity patterns. We developed an atlas of wildfire severity across south-eastern Australia between 1988 and 2020 to test (a) whether the 2019/2020 fire season was more severe than previous fire seasons, and (b) if the proportion of high-severity fire within the burn extent (HSp) increases with wildfire size and annual area burnt. We demonstrate that the 2019/2020 wildfires in south-eastern Australia were generally greater in extent but not proportionally more severe than previous fires, owing to constant scaling between HSp and annual fire extent across the dominant dry-forest communities. However, HSp did increase with increasing annual fire extent across wet-forests and the less-common rainforest and woodland communities. The absolute area of high-severity fire in 2019/2020 (∼1.8 M ha) was larger than previously seen, accounting for ∼44% of the area burnt by high-severity fire over the past 33 years. Our results demonstrate that extreme fire seasons are a rare but defining feature of fire regimes across forested regions, owing to the disproportionate influence of mega-fires on area burnt.