Na-Ion Battery Anodes: Materials and Electrochemistry

Abstract

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.

Metallic Sn‐Based Anode Materials: Application in High‐Performance Lithium‐Ion and Sodium‐Ion Batteries

“…Although the theoretical specific capacity of Sn is not the highest among them, the volumetric specific capacity of Sn is quite close to those of Si and Ge. Moreover, the Sn and Sn‐based compounds have been heavily researched due to their merits of high availability, low cost, and high electrical conductivity 12, 13, 14, 15, 16. In 2005, Sony corporation announced the commercialization of a new type of lithium‐ion battery, named “Nexelion,” which was the first to use an amorphous Sn–Co–C composite as a negative electrode, and led to a 30% volumetric capacity increase over conventional LIBs 17, 18.…”

Large‐Area Carbon Nanosheets Doped with Phosphorus: A High‐Performance Anode Material for Sodium‐Ion Batteries

“…In view of the successful application of carbon material in LIBs, carbon material has been supposed to be a promising electrode candidate for SIBs 2. Because Na + ions cannot be easily intercalated into the layers of graphite due to larger radius of Na + , resulting in a low capacity of 31 mAh g −1 , conventional graphite might not be suitable for SIBs 3. However, various amorphous carbon materials including hollow nanostructured carbons,4 carbon nanospheres,5 carbon nanofibres,6 carbon nanosheets,7 porous carbons,8 hard carbon,9 graphene,10 and heteroatom‐doped carbon materials11 are being investigated as anode for SIBs in full swing, benefiting from disordered nanodomains with randomly oriented graphene layers and voids between these domains, which can provide rich active sites for storing Na + 9, 12.…”

High‐Performance and Low‐Cost Sodium‐Ion Anode Based on a Facile Black Phosphorus−Carbon Nanocomposite

“…Sodium ion batteries (SIBs) attract increasing research attention because of the high abundance of sodium compared to lithium, and significant progress has been made in recent years. [1][2][3] Among the high-capacity anode materials (Sb, Sn, etc.) for sodium ion storage, phosphorus exhibits the highest theoretical capacity of 2596 mAh g −1 (Na 3 P).…”

“…The BP-C composite still contains both sp 2 and sp 3 carbon, but the intensity of the sp 2 carbon signal is lower, possibly due to a lower level of graphitization in the sample due to the high-energy ball milling. The electrochemical performance of the BP-C composite anode (Figure 3) was evaluated within half-cell SIBs.…”