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This review focuses on carbon-based sodium ion battery (NIB) negative electrodes, emphasizing the internal structure – Na storage mechanisms – electrochemical performance relations. We bring a unique vantage to the ever-expanding field of NIB anode literature: To quantify the critical emphasis on the structure – properties interdependence, we provide comprehensive data comparisons of representative published studies. This is accomplished through a series of “Master Plots”, which rather than focusing on an individual publication, combine the data by broad features first outlined in the taxonomy section. The advantage of such an approach is that it transcends the paper-to-paper differences in electrochemical performance in a given class of anodes, providing generalizable comparisons that are statistically significant. For instance, we manage to demonstrate that, while N-doped carbons have a slight advantage in terms of capacity, their rate performance at higher currents is unchanged over that of undoped carbons. To our knowledge such broad high-level data analysis has not been done in past reviews on either NIB or LIB carbon anodes. Furthermore, we also discuss a wide range of individual microstructures and chemistries, offering critical analysis when appropriate. [ABSTRACT FROM AUTHOR]

Hard carbon is the leading candidate anode for commercialization of Na-ion batteries. Hard carbon has a unique local atomic structure, which is composed of nanodomains of layered rumpled sheets that have short-range local order resembling graphene within each layer, but complete disorder along the c-axis between layers. A primary challenge holding back the development of Na-ion batteries is that a complete understanding of the structure-capacity correlations of Na-ion storage in hard carbon has remained elusive. This article presents two key discoveries: first, the characteristics of hard carbons structure can be modified systematically by heteroatom doping, and second, that these structural changes greatly affect Na-ion storage properties, which reveals the mechanisms for Na storage in hard carbon. Specifically, via P or S doping, the interlayer spacing is dilated, which extends the low-voltage plateau capacity, while increasing the defect concentrations with P or B doping leads to higher sloping sodiation capacity. The combined experimental studies and first principles calculations reveal that it is the Na-ion-defect binding that corresponds to the sloping capacity, while the Na intercalation between graphenic layers causes the low-potential plateau capacity. The understanding suggests a new design principle of hard carbon anode: more reversibly binding defects and dilated turbostratic domains, given that the specific surface area is maintained low. [ABSTRACT FROM AUTHOR]

Graphite is the commercial anode for lithium-ion batteries; however, it fails to extend its success to sodium-ion batteries. Recently, we demonstrated that a low-cost amorphous carbon soft carbon exhibits remarkable rate performance and stable cycling life of Na-ion storage. However, its Na-ion storage mechanism has remained elusive, which has plagued further development of such carbon anodes. Here, we remedy this shortfall by presenting the results from an integrated set of experimental and computational studies that, for the first time, reveal the storage mechanism for soft carbon. We find that sodium ions intercalate into graphenic layers, leading to an irreversible quasi-plateau at ∼0.5 V versus Na+/Na as well as an irreversible expansion seen by in situ transmission electron microscopy (TEM) and X-ray diffraction (XRD). Such a high-potential plateau is correlated to the defective local structure inside the turbostratic stacking of soft carbon and the associated high-binding energies with Na ions, suggesting a trapping mechanism. On the other hand, soft carbon exhibits long sloping regions above and below the quasi-plateau during the first sodiation, where the sloping regions present highly reversible behavior. It is attributed to the more defects contained by soft carbon revealed by neutron total scattering and the associated pair distribution function studies. [ABSTRACT FROM AUTHOR]

The rate capability of hard carbon has long been underestimated in prior studies that used carbon/Na two-electrode half-cells. Through a three-electrode cell setup, we discover that it is the overpotential of the sodium counter electrode that drives the half-cells to the lower cutoff potential prematurely during hard carbon sodiation, particularly at high current rates, which prevents the hard carbon anode from being fully sodiated. [ABSTRACT FROM AUTHOR]

Hard carbon microspheres (HCS) exhibit a highly reversible capacity of 262 mAh g−1 for K‐ion batteries. They present a superior rate capability for K‐ions to Na‐ions, where at 2C, HCS/K cells deliver 190 mAh g−1 in contrast to 97 mAh g−1 from HCS/Na cells. It is determined that the K‐ion diffusion coefficient of HCS is higher than that of Na‐ions. [ABSTRACT FROM AUTHOR]

Abstract: We report an inverse relationship between measurable porosity values and reversible capacity from sucrose-derived hard carbon as an anode for sodium-ion batteries (SIBs). Materials with low measureable pore volumes and surface areas obtained through N2 sorption yield higher reversible capacities. Conversely, increasing measurable porosity and specific surface area leads to sharp decreases in reversible capacity. Utilizing a low porosity material, we thus are able to obtain a reversible capacity of 335mAhg− 1. These findings suggest that sodium-ion storage is highly dependent on the absence of pores detectable through N2 sorption in sucrose-derived carbon. [Copyright &y& Elsevier]

A front cover of the periodical Advanced Materials Interfaces of October 6, 2016 issue is presented.

In article number 1501874, Xiulei Ji and co‐workers investigate hard carbon microspheres as hard carbon anode materials for potassium‐ion batteries. K‐ions diffuse faster than Na‐ions in the defective, card‐house modeled structure of hard carbon, resulting in much better rate capability of hard carbon anode in future K‐ion batteries than in Na‐ion batteries. Image designed by Clement Bommier. [ABSTRACT FROM AUTHOR]

Review: [124 refs. [ABSTRACT FROM AUTHOR]

The intermittent nature of renewable energy sources, such as solar and wind, calls for sustainable electrical energy storage (EES) technologies for stationary applications. Li will be simply too rare for Li-ion batteries (LIBs) to be used for large-scale storage purposes. In contrast, Na-ion batteries (NIBs) are highly promising to meet the demand of grid-level storage because Na is truly earth abundant and ubiquitous around the globe. Furthermore, NIBs share a similar rocking-chair operation mechanism with LIBs, which potentially provides high reversibility and long cycling life. It would be most efficient to transfer knowledge learned on LIBs during the last three decades to the development of NIBs. Following this logic, rapid progress has been made in NIB cathode materials, where layered metal oxides and polyanionic compounds exhibit encouraging results. On the anode side, pure graphite as the standard anode for LIBs can only form NaC64 in NIBs if solvent co-intercalation does not occur due to the unfavorable thermodynamics. In fact, it was the utilization of a carbon anode in LIBs that enabled the commercial successes. Anodes of metal-ion batteries determine key characteristics, such as safety and cycling life; thus, it is indispensable to identify suitable anode materials for NIBs. In this Account, we review recent development on anode materials for NIBs. Due to the limited space, we will mainly discuss carbon-based and alloy-based anodes and highlight progress made in our groups in this field. We first present what is known about the failure mechanism of graphite anode in NIBs. We then go on to discuss studies on hard carbon anodes, alloy-type anodes, and organic anodes. Especially, the multiple functions of natural cellulose that is used as a low-cost carbon precursor for mass production and as a soft substrate for tin anodes are highlighted. The strategies of minimizing the surface area of carbon anodes for improving the first-cycle Coulombic efficiency are also outlined, where graphene oxide was employed as dehydration agent and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was used to unzip wood fiber. Furthermore, surface modification by atomic layer deposition technology is introduced, where we discover that a thin layer of Al2O3 can function to encapsulate Sn nanoparticles, leading to a much enhanced cycling performance. We also highlight recent work about the phosphorene/graphene anode, which outperformed other anodes in terms of capacity. The aromatic organic anode is also studied as anode with very high initial sodiation capacity. Furthermore, electrochemical intercalation of Na ions into reduced graphene oxide is applied for fabricating transparent conductors, demonstrating the great feasibility of Na ion intercalation for optical applications. [ABSTRACT FROM AUTHOR]