Prospective Article Nanostructured layered vanadium oxide as cathode for high-performance sodium-ion batteries: a perspective Wen Luo, State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China; Laboratoire de Chimie et Physique: Approche Multi-échelles des Milieux Complexes, Institut Jean Barriol, Université de Lorraine, Metz 57070, France Jean-Jacques Gaumet, Laboratoire de Chimie et Physique: Approche Multi-échelles des Milieux Complexes, Institut Jean Barriol, Université de Lorraine, Metz 57070, France Liqiang Mai, State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China; Department of Chemistry, University of California, Berkeley, California 94720, USA Address all correspondence to Jean-Jacques Gaumet at jean-jacques.gaumet@univ-lorraine.fr and Liqiang Mai at mlq518@whut.edu.cn (Received 22 January 2017; accepted 7 April 2017) Abstract Sodium-ion batteries (SIBs) have received intensive attentions owing to the abundant and inexpensive sodium (Na) resource. Layered vana- dium oxides are featured with various valence states and corresponding compounds, and through multi-electron reaction they are capable to deliver high Na storage capacity. The rational construction of unique structures is verified to improve their Na storage properties. This per- spective provides an overview of recent advances in layered vanadium oxide for SIBs, with a particular focus on construction of novel nano- structures, and mechanism studies via in situ characterization. Finally, we predict possible breakthroughs and future trends that lie ahead for high-performance layered vanadium oxides SIBs cathode. Introduction Recently, there are increasing concerns of sustainable energy and environment due to the growing consumption of non- renewable fossil fuels. The urgent requirement for clean and renewable energy sources has stimulated the rapid development of efficient, stable and reliable electricity supply systems. Lithium-ion batteries (LIBs) have been widely utilized in mod- ern society such as in portable electronic device, electrical vehi- cles (EVs), and large-scale grid. [1–3] Recently, with the great concerns about the limited lithium (Li) resource, sodium-ion batteries (SIBs) have emerged as one of promising alternatives to LIBs due to its abundant and inexpensive sodium (Na) resource. [4,5] Meanwhile, Na has been studied to exhibit suit- able redox potential and similar intercalation chemistry to Li; thus, SIBs hold promise to be viable complement or replace- ment to LIBs as the next-generation energy storage device. [6,7] However, the larger radius of Na + ions requires an expanding host space when a typical sodiation/desodiation process occurs. Consequently the size effect of Na + ions would result in severe damage on the lattice structure of the host. Besides, Na + ions are demonstrated to exhibit lower diffusion rate compared with Li + ions. Therefore, the understanding and development of reliable cathode with suitable lattice space to host Na + ions are the key issues to be addressed. Vanadium oxides feature unique open-layered structures, which allow a diversity of other cations or molecules to insert into the layers. [8,9] In LIBs, these open-layered structures are capable to accommodate more Li + ions, thus give rise to higher specific capacity than those of the commercial cathodes. [10] Moreover, vanadium oxides display rich redox chemistry due to different oxidation states and coordination geometries, there- fore resulting in their different valence states and phase struc- tures. With concerns to their layered structures, vanadium oxides generally contain [VO 6 ] octahedral geometry with less [VO 4 ] tetrahedron. Basically, these octahedral can form two- dimensional (2D) sheet structures by sharing edges and/or corners (sometimes faces). [11] These octahedral or tetrahedron possessed with a long V–O bond (2.1–2.6 Å, and 2.79 Å in V 2 O 5 itself) and a short vanadyl bond, –V = O (1.55–1.75 Å) are capable to form various layered structures (Fig. 1). As depicted in literature, a double chain of edge-sharing [VO 6 ] octahedral is the basic assembly unit. When the double chains are congregated by sharing the side corners, and a single layer can occur in most vanadium oxides [Fig. 1(a)]. In orthorhombic α-V 2 O 5 [Fig. 1(b)], a short vanadyl bond and the other longer V–O bonds coexist. Consequently, the vanadium coordination polyhedron changes into a square pyramid due to the longer weak bond [weak V–O bond illustrated in Fig. 1(c)]. [11] As sug- gested by Sohn et al., when these (V 2 O 4 ) n chains closely aligned by sharing edges, no-vacancy square-pyramidal layered VO 2 is formed [Fig. 1(f)]. [12] V 6 O 13 structure is formed by sin- gle and double layers sharing corners alternatively [Fig. 1 (e)]. [13] When all the apices (vanadyl bonds) emerge up in one layer and also down in the other layers, a typical double MRS Communications (2017), 7, 152–165 © Materials Research Society, 2017 doi:10.1557/mrc.2017.25 152 ▪ MRS COMMUNICATIONS • VOLUME 7 • ISSUE 2 • www.mrs.org/mrc https://doi.org/10.1557/mrc.2017.25 Downloaded from https://www.cambridge.org/core. IP address: 54.162.69.248, on 20 May 2020 at 09:19:41, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.