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Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations
Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations
Sodium ion batteries are an emerging candidate to replace lithium ion batteries in large-scale electrical energy storage systems due to the abundance and widespread distribution of sodium. Despite the growing interest, the development of high-performance sodium cathode materials remains a challenge. In particular, polyanionic compounds are considered as a strong cathode candidate owing to their better cycling stability, a flatter voltage profile, and stronger thermal stability compared to other cathode materials. Here, we report the rational design of a biomimetic bone-inspired polyanionic Na3V2(PO4)3-reduced graphene oxide composite (BI-NVP) cathode that achieves ultrahigh rate charging and ultralong cycling life in a sodium ion battery. At a charging rate of 1 C, BI-NVP delivers 97% of its theoretical capacity and is able to retain a voltage plateau even at the ultra-high rate of 200 C. It also shows long cycling life with capacity retention of 91% after 10 000 cycles at 50 C. The sodium ion battery cells with a BI-NVP cathode and Na metal anode were able to deliver a maximum specific energy of 350 W h kg−1 and maximum specific power of 154 kW kg−1. In situ and postmortem analyses of cycled BI-NVP (including by Raman and XRD spectra) HRTEM, and STEM-EELS, indicate highly reversible dilation–contraction, negligible electrode pulverization, and a stable NVP-reduced graphene oxide layer interface. The results presented here provide a rational and biomimetic material design for the electrode architecture for ultrahigh power and ultralong cyclability of the sodium ion battery full cells when paired with a sodium metal anode.
In this work, repeated cold rolling and folding is employed to fabricate a metallurgical composite of sodium–antimony–telluride Na 2 (Sb 2/6 Te 3/6 Vac 1/6 ) dispersed in electrochemically active sodium metal, termed “NST-Na.” This new intermetallic has a vacancy-rich thermodynamically stable face-centered-cubic structure and enables state-of-the-art electrochemical performance in widely employed carbonate and ether electrolytes. NST-Na achieves 100% depth-of-discharge (DOD) in 1 m NaPF 6 in G2, with 15 mAh cm –2 at 1 mA cm –2 and Coulombic efficiency (CE) of 99.4%, for 1000 h of plating/stripping. Sodium-metal batteries (SMBs) with NST-Na and Na 3 V 2 (PO 4 ) 3 (NVP) or sulfur cathodes give significantly improved energy, cycling, and CE (>99%). An anode-free battery with NST collector and NVP obtains 0.23% capacity decay per cycle. Imaging and tomography using conventional and cryogenic microscopy (Cryo-EM) indicate that the sodium metal fills the open space inside the self-supporting sodiophilic NST skeleton, resulting in dense (pore-free and solid electrolyte interphase (SEI)-free) metal deposits with flat surfaces. The baseline Na deposit consists of filament-like dendrites and “dead metal”, intermixed with pores and SEI. Density functional theory calculations show that the uniqueness of NST lies in the thermodynamic stability of the Na atoms (rather than clusters) on its surface that leads to planar wetting, and in its own stability that prevents decomposition during cycling.
Na3V2(PO4)2F3 crystallizes in the orthorhombic Pnnm space group. The structure is three-dimensional. there are three inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a 7-coordinate geometry to four O2- and three F1- atoms. There are two shorter (2.43 Å) and two longer (2.68 Å) Na–O bond lengths. There are two shorter (2.48 Å) and one longer (2.61 Å) Na–F bond lengths. In the second Na1+ site, Na1+ is bonded in a 4-coordinate geometry to four O2- and three F1- atoms. There are two shorter (2.42 Å) and two longer (2.95 Å) Na–O bond lengths. There are two shorter (2.42 Å) and one longer (2.75 Å) Na–F bond lengths. In the third Na1+ site, Na1+ is bonded in a 7-coordinate geometry to four O2- and three F1- atoms. There are two shorter (2.44 Å) and two longer (2.51 Å) Na–O bond lengths. There are one shorter (2.47 Å) and two longer (2.48 Å) Na–F bond lengths. V3+ is bonded to four O2- and two F1- atoms to form VO4F2 octahedra that share a cornercorner with one VO4F2 octahedra and corners with four PO4 tetrahedra. The corner-sharing octahedral tilt angles are 2°. There are a spread of V–O bond distances ranging from 1.99–2.07 Å. Both V–F bond lengths are 2.02 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with four equivalent VO4F2 octahedra. The corner-sharing octahedra tilt angles range from 43–45°. All P–O bond lengths are 1.55 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with four equivalent VO4F2 octahedra. The corner-sharing octahedra tilt angles range from 43–44°. There is two shorter (1.54 Å) and two longer (1.55 Å) P–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to two Na1+, one V3+, and one P5+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two Na1+, one V3+, and one P5+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to one Na1+, one V3+, and one P5+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Na1+, one V3+, and one P5+ atom. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a 4-coordinate geometry to three Na1+ and one V3+ atom. In the second F1- site, F1- is bonded in a 2-coordinate geometry to three Na1+ and two equivalent V3+ atoms.