Hard carbons have shown considerable promise as anodes for emerging sodium-ion battery technologies. Current understanding of sodium-storage behaviour in hard carbons attributes capacity to filling of graphitic interlayers and pores,...

A series of hard-soft carbon composite materials is produced from biomass and oil waste and applied as low-cost anodes for sodium-ion batteries to study the fundamentals behind the dependence of Na storage on their structural features. A good reversible capacity of 282 mAh g −1 is obtained at a current density of 30 mA g −1 with a high initial Coulombic efficiency of 80% at a carbonization temperature of only 1000 °C by adjusting the ratio of hard to soft carbon. The performance is superior to the pure hard or soft carbon anodes produced at the same temperatures. This synergy between hard and soft carbon resulting in an excellent performance is due to the blockage of some open pores in hard carbon by the soft carbon, which suppresses the solid electro lyte interface formation and increases the reversible sodium storage capacity.

Increasing concerns regarding the sustainability of lithium sources, due to their limited availability and consequent expected price increase, have raised awareness of the importance of developing alternative energy-storage candidates that can sustain the ever-growing energy demand. Furthermore, limitations on the availability of the transition metals used in the manufacturing of cathode materials, together with questionable mining practices, are driving development towards more sustainable elements. Given the uniformly high abundance and cost-effectiveness of sodium, as well as its very suitable redox potential (close to that of lithium), sodium-ion battery technology offers tremendous potential to be a counterpart to lithium-ion batteries (LIBs) in different application scenarios, such as stationary energy storage and low-cost vehicles. This potential is reflected by the major investments that are being made by industry in a wide variety of markets and in diverse material combinations. Despite the associated advantages of being a drop-in replacement for LIBs, there are remarkable differences in the physicochemical properties between sodium and lithium that give rise to different behaviours, for example, different coordination preferences in compounds, desolvation energies, or solubility of the solid–electrolyte interphase inorganic salt components. This demands a more detailed study of the underlying physical and chemical processes occurring in sodium-ion batteries and allows great scope for groundbreaking advances in the field, from lab-scale to scale-up. This roadmap provides an extensive review by experts in academia and industry of the current state of the art in 2021 and the different research directions and strategies currently underway to improve the performance of sodium-ion batteries. The aim is to provide an opinion with respect to the current challenges and opportunities, from the fundamental properties to the practical applications of this technology.

Introduced in the literature in 1913 by Bergius, who at the time was studying biomass coalification, Hydrothermal Carbonisation, as many other technologies based on renewables, has been forgotten during the...

Batteries that extend performance beyond the intrinsic limits of Li-ion batteries are among the most important developments required to continue the revolution promised by electrochemical devices. Of these next-generation batteries, lithium sulfur (Li–S) chemistry is among the most commercially mature, with cells offering a substantial increase in gravimetric energy density, reduced costs and improved safety prospects. However, there remain outstanding issues to advance the commercial prospects of the technology and benefit from the economies of scale felt by Li-ion cells, including improving both the rate performance and longevity of cells. To address these challenges, the Faraday Institution, the UK’s independent institute for electrochemical energy storage science and technology, launched the Lithium Sulfur Technology Accelerator (LiSTAR) programme in October 2019. This Roadmap, authored by researchers and partners of the LiSTAR programme, is intended to highlight the outstanding issues that must be addressed and provide an insight into the pathways towards solving them adopted by the LiSTAR consortium. In compiling this Roadmap we hope to aid the development of the wider Li–S research community, providing a guide for academia, industry, government and funding agencies in this important and rapidly developing research space.

Hard carbons are among the most promising materials for alkali-ion metal anodes. These materials have a highly complex structure and understanding the metal storage and migration within these structures is of utmost importance for the development of next-generation battery technologies. The effect of different carbon structural motifs on Li, Na, and K storage and diffusion are probed using density functional theory based on experimental characterizations of hard carbon samples. Two carbon structural models-the planar graphitic layer model and the cylindrical pore model-are constructed guided by small-angle X-ray scattering and transmission electron microscopy characterization. The planar graphitic layers with interlayer distance <6.5 Å are beneficial for metal storage, but do not have significant contribution to rapid metal diffusion. Fast diffusion is shown to take place in planar graphitic layers with interlayer distance >6.5 Å, when the graphitic layer separation becomes so wide that there is negligible interaction between the two graphitic layers. The cylindrical pore model, reflecting the curved morphology, does not increase metal storage, but significantly lowers the metal migration barriers. Hence, the curved carbon morphologies are shown to have great importance for battery cycling. These findings provide an atomic-scale picture of the metal storage and diffusion in these materials.

Hard carbons, due to their relatively low cost and good electrochemical performance, are considered the most promising anode materials for Na-ion batteries. Despite the many reported structures of hard carbon, the practical use of hard carbon anodes is largely limited by low initial Coulombic efficiency (ICE) and the sodium storage mechanism still remains elusive. A better understanding of the sodium ion behaviour in hard carbon anodes is crucial to develop more efficient sodium ion batteries. Here, a series of hard carbon materials with tailored morphology and surface functionality was synthesized via hydrothermal carbonisation and subsequent pyrolysis from 1000 to 1900 °C. Electrochemical results revealed different sodiation-desodiation trends in the galvanostatic potential profiles and varying ICE, and were compared with theoretical studies to understand the effect of the varying hard carbon structure on the sodium storage process at different voltages. Furthermore, electrode expansion during cycling was investigated by in-situ dilatometry; to the best of our knowledge, this is the first time the technique has been applied to hard carbons for ion storage mechanism investigation in Na-ion batteries. Combining experimental and theoretical results, we propose a model for sodium storage in our hard carbons that consists of Na-ion storage at defect sites and by intercalation in the high voltage slope region and via pore-filling in the low voltage plateau

Graphene nanoplatelets (GNP) were exfoliated using a nondestructive chemical reduction method and subsequently decorated with polymers using two different approaches: graf ting f rom and graf ting to. Poly(methyl methacrylate) (PMMA) with varying molecular weights was covalently attached to the GNP layers using both methods. The grafting ratios were higher (44.6% to 126.5%) for the graf ting f rom approach compared to the grafting to approach (12.6% to 20.3%). The products were characterized using thermogravimetric analysis−mass spectrometry (TGA-MS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The graf ting f rom products showed an increase in the grafting ratio and dispersibility in acetone with increasing monomer supply; on the other hand, due to steric effects, the graf ting to products showed lower absolute grafting ratios and a decreasing trend with increasing polymer molecular weight. The excellent dispersibility of the grafting f rom functionalized graphene, 900 μg/mL in acetone, indicates an increased compatibility with the solvent and the potential to increase graphene reinforcement performance in nanocomposite applications.