Experimental and Computational Investigation of Lepidocrocite Anodes for Sodium-Ion Batteries

Abstract

In this work, we investigated several titanates with lepidocrocite-type structures (general formula A x Ti 1−y M y O 4 with A=Na and M=Li or Mg), having potential utility as anode materials for sodium-ion batteries. First principles calculations were used to determine key battery metrics, including potential profiles, structural changes during sodiation, and sodium diffusion energy barriers for several compositions, and compared to experimental results. Site limitations were found to be critical determinants of the gravimetric capacities, which are also affected both by the stacking arrangement of the

A layered nonstoichiometric lepidocrocite-type sodium titanate anode material for sodium-ion batteries

“…The gravimetric capacities of lepidocrocite titanates are generally limited by the number of available sites for ion intercalation rather than the amount of reducible Ti ions. 12 The theoretical capacity of NTO is 201 mAh g -1 if considering only the number of interlayer sites, less than the obtained capacity of 229 mAh g -1 . However, an augmented capacity of 230 mAh g -1 can be expected from NTO if the titanium vacancies are also considered.…”

“…8 Depending on structure (layered or tunnel), a considerable amount of Na + can be reversibly stored (e.g., 200 mAh g -1 for sodium nonatitanate) 9 at low potentials (in the range of 0.3 ~ 0.6 V vs. Na + /Na). 5,10,11 We recently reported on several candidate sodium titanate anodes 5,9,11,12 with lepidocrocite-type structures. These materials have the general formula Na x Ti 2-y M y O 4 (where M represents a variety of substituents such as Li + or Mg 2+ ).…”

“…13 A computational study indicated that both interlayer site limitations and electrostatic considerations govern the capacity that can be obtained practically, particularly for C-type structures. 12 The presence of a mobile cation such as Li in the metal oxide layer provides an additional diffusional pathway for sodium and also improves practical capacities at a given rate; Mg-substituted titanates, in contrast, perform very poorly. This observation motivated us to look for phases with vacancies in the metal oxide layers, on the assumption that these vacancies will have similar beneficial effects as mobile cations.…”

Heterostructured Lepidocrocite Titanate-Carbon Nanosheets for Electrochemical Applications

“…Lepidocrocite-type titanates have the general formula of AxTi2−y MyO4, where A = K, Rb, or Cs, and M represents Li, Mg, Mn, Fe, Co, Ni, Cu, Zn or a vacancy. 9,[14][15][16] Zigzag-type layered structures of lepidocrocite titanates consist of edge and corner-shared TiO6 octahedra where A cations are located between the transition metal layers and M cations reside within layers. Recently, we have demonstrated sodium and lithium intercalation into lepidocrocite-type potassium titanate (K0.8Ti1.73Li0.27O4, KTL).…”

Optimization of nonatitanate electrodes for sodium-ion batteries

“…[12][13][14] Recently, our group has described several types of intercalation anodes based on sodium titanates with low potentials and high capacities. [15][16][17][18][19] These materials are denser than carbon and have smaller volume changes than the alloys, therefore, full utilization of sodium titanates in a sodium-ion battery may lead to higher energy density, better cycling stability, and improved safety over the options listed above.…”