Results for “NaSi” | Engineering Papers

DOE OSTI2020

Materials Data on NaSi by Materials Project

NaSi crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are two inequivalent Na sites. In the first Na site, Na is bonded in a 3-coordinate geometry to six Si atoms. There are a spread of Na–Si bond distances ranging from 3.01–3.40 Å. In the second Na site, Na is bonded in a 4-coordinate geometry to five Si atoms. There are a spread of Na–Si bond distances ranging from 2.88–3.31 Å. There are two inequivalent Si sites. In the first Si site, Si is bonded in a 9-coordinate geometry to six Na and three Si atoms. There are a spread of Si–Si bond distances ranging from 2.40–2.48 Å. In the second Si site, Si is bonded in a 8-coordinate geometry to five Na and three Si atoms. The Si–Si bond length is 2.42 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Design of a Single-Ion Conducting Polymer Electrolyte for Sodium-Ion Batteries

Here, a sodium bis(fluoroallyl)malonato borate salt (NaBFMB) is synthesized. Using a Click thiol-ene reaction, NaBFMB can be photo-crosslinked with a tri-thiol (trimethylolpropane tris(3-mercapto propionate), TMPT) to create a single-ion conducting electrolyte (NaSIE), with all negative charges residing on the borate moieties and anions immobilized through the 3-D crosslinked network. The NaSIE can be prepared either as a free-standing film or through a drop-cast method followed by a photo crosslinking method for an in-situ formation on top of the electrodes. The free-standing film of NaSIE has a high ionic conductivity of 2 × 10 –3 S cm –1 at 30 °C, and a high transference number (t Na + ) of 0.91 as measured through the Bruce-Vincent method. The electrochemical stability of NaSIE polymer electrolyte is demonstrated via cyclic voltammetry (CV) to be stable up to 5 V vs Na/Na + . When tested inside a symmetrical Na//Na cell, the NaSIE shows a critical current density (CCD) of 0.4 mA cm –2 . The stability of NaSIE is further demonstrated via a long cycling of the stripping/plating test with a current density of 0.1 mA cm –2 at five-minute intervals for over 10,000 min. Using the in-situ method, NaSIE is used as the electrolyte for a sodium metal battery using P2 (Na resides at prismatic sites with with ABBAAB stacking)-cathode of Na 0.67 Ni 0.33 Mn 0.67 O 2 (NNMO) and is cycled between the cut-off voltages of 2.0–4.0 V. A high initial specific capacity (85.7 mAh g –1 ) with a capacity retention of 86.79% after 150 cycles is obtained.

25 ENERGY STORAGE↗