Structure and function of hard carbon negative electrodes for sodium-ion batteries

Abstract

Practical utilisation of renewable energy from intermittent sustainable sources such as solar and wind relies on safe, reliable, cost-effective, and high-capacity energy storage systems to be incorporated in the grid. Among the most promising technologies aimed towards this application are sodium-ion batteries. Currently, hard carbon is the leading negative electrode material for sodium-ion batteries given its relatively good electrochemical performance and low cost. Furthermore, hard carbon can be produced from a diverse range of readily available waste and renewable biomass sources making this an ideal material for the circular economy. In facilitating future developments on the use of hard carbon-based electrode materials for sodium-ion batteries, this review curates several analytical techniques that have been useful in providing structure-property insight and stresses the need for overall assessment to be based on a combination of complementary techniques. It also emphasises several key challenges in the characterisation of hard carbons and how various in situ and operando techniques can help unravel those challenges by providing us with a better understanding of these systems during operation thereby allowing us to design high-performance hard carbon materials for next-generation batteries.

Unravelling Charge Storage Mechanisms of Lithium, Sodium and Potassium into Graphene‐Coffee Waste Derived Hard Carbon Composites

“…biowaste-derived hard carbons reported in literature which are in the range of 3.7-4.2 Å. [49] This could be ascribed to the reduction of the disorder degree in the sample due to the addition of graphene as observed in our previous work. [43] The crystallite size along the c-axis (L c ) and the size of the layer planes (L a ) were 13.42 and 64.04 Å, respectively, as calculated by the Scherrer's equation.…”

“…According to Bragg's Law the interlayer distance ( d 002 ) of rGOCOF corresponds to 3.50 Å, which is slightly higher than the graphene interlayered distance in graphite (3.35 Å). It is worth to remark that the interlayer distance of the graphene‐coffee waste hard carbon is slightly lower when compared to other biowaste‐derived hard carbons reported in literature which are in the range of 3.7–4.2 Å [49] . This could be ascribed to the reduction of the disorder degree in the sample due to the addition of graphene as observed in our previous work [43] .…”

Reconfiguring Hard Carbons with Emerging Sodium‐Ion Batteries: A Perspective

“…[83] Copyright 2016, The Royal Society of Chemistry. e) 23 Na magic angle spinning NMR and EPR spectra of hard carbons at various discharge points. Reproduced with permission.…”

“…However, the narrow peak centered at g = 2.002 is caused by the formation of metallic sodium. [159] Operando 23 Na ssNMR was used by Stratford et al to provide insight into the sodiation process, and showed that sodium ions are first adsorbed on the carbon surfaces in the sloping region followed by the formation of quasi-metallic clusters at the plateau region (Figure 9d). [83] Au et al used ex situ 23 Na ssNMR and total scattering to study the [162] Copyright 2017, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.…”

“…Fortunately, hard carbon anodes in SIBs show similar electrochemical performance to the graphite anode in LIBs, namely long and reversible low-potential charge/discharge plateaus (<0.1 V). [21][22][23][24] Stevens et al first reported that glucose-derived hard carbons possess a reversible capacity of ≈300 mAh g −1 , over half of which came from the plateau. [25] Since then, researchers have extensively investigated different hard carbons prepared from various precursors and with different synthesis conditions, and these have posed a great problem concerning the sodium storage mechanism and how to design ideal hard carbon anodes for commercialization.…”