posted on 2021-09-28, 14:04authored byZane Grady, Zhongming Fan, Arnaud Ndayishimiye, Clive A. Randall
Electrodes
for solid-state batteries require the conduction of
both ions and electrons for extraction of the energy from the active
material. In this study, we apply cold sintering to a model composite
cathode system to study how low-temperature densification enables
a degree of control over the mixed conducting properties of such systems.
The model system contains the NASICON-structured Na3V2(PO4)3 (NVP) active material, NASICON-structured
solid electrolyte (Na3Zr2Si2PO12, NZSP), and electron-conducting carbon nanofiber (CNF).
Pellets of varying weight fractions of components were cold-sintered
to greater than 90% of the theoretical density at 350–375 °C,
a 360 MPa uniaxial pressure, and with a 3 h dwell time using sodium
hydroxide as the transient sintering aid. The bulk conductivity of
the diphasic composites was measured with impedance spectroscopy;
the total conductivities of the composites are increased from 3.8
× 10–8 S·cm–1 (pure
NVP) to 5.81 × 10–6 S·cm–1 (60 wt % NZSP) and 1.31 × 10–5 S·cm–1 (5 wt % CNF). Complimentary direct current polarization
experiments demonstrate a rational modulation in transference number
(τ) of the composites; τ of pure NVP = 0.966, 60 wt %
NZSP = 0.995, and 5 wt % CNF = 0.116. Finally, all three materials
are combined into triphasic composites to serve as solid-state cathodes
in a half-cell configuration with a liquid electrolyte. Electrochemical
activity of the active material is maintained, and the capacity/energy
density is comparable to prior work.