Assessing the Electrochemical Stability Window of NASICON-Type Solid Electrolytes

Abstract

All-Solid-State Lithium Batteries (ASSLBs) are promising since they may enable the use of high potential materials as positive electrode and lithium metal as negative electrode. This is only possible through solid electrolytes (SEs) stated large electrochemical stability window (ESW). Nevertheless, reported values for these ESWs are very divergent in the literature. Establishing a robust procedure to accurately determine SEs’ ESWs has therefore become crucial. Our work focuses on bringing together theoretical results and an original experimental set up to assess the electrochemical stability window of the two NASICON-type SEs Li1.3Al0.3Ti1.7(PO4)3 (LATP) and Li1.5Al0.5Ge1.5(PO4)3 (LAGP). Using first principles, we computed thermodynamic ESWs for LATP and LAGP and their decomposition products upon redox potentials. The experimental set-up consists of a sintered stack of a thin SE layer and a SE-Au composite electrode to allow a large contact surface between SE and conductive gold particles, which maximizes the redox currents. Using Potentiostatic Intermittent Titration Technique (PITT) measurements, we were able to accurately determine the ESW of LATP and LAGP solid electrolytes. They are found to be [2.65–4.6 V] and [1.85–4.9 V] for LATP and LAGP respectively. Finally, we attempted to characterize the decomposition products of both materials upon oxidation. The use of an O2 sensor coupled to the electrochemical setup enabled us to observe operando the production of O2 upon LAGP and LATP oxidations, in agreement with first-principles calculations. Transmission Electron Microscopy (TEM) allowed to observe the presence of an amorphous phase at the interface between the gold particles and LAGP after oxidation. Electrochemical Impedance Spectroscopy (EIS) measurements confirmed that the resulting phase increased the total resistance of LAGP. This work aims at providing a method for an accurate determination of ESWs, considered a key parameter to a successful material selection for ASSLBs.

NMR Study of Lithium Transport in Liquid–Ceramic Hybrid Solid Composite Electrolytes

“…The obtained suspension was subsequently dried, ground to micrometer-sized particles, and heated to 900 °C for 6 h. Phase purity was confirmed via XRD (Figure S1). The LATP pellet used for ionic conductivity measurements was sintered via spark plasma sintering …”

“…The LATP pellet used for ionic conductivity measurements was sintered via spark plasma sintering. 14 LLZO was prepared via a solid-state process. Prior to weighing, the La 2 O 3 precursor was fired at 600 °C overnight and then stored in a glovebox due to its hygroscopic nature.…”

“…However, these materials present several challenges for widespread use in ASSLBs due to the associated safety concerns, the need for maintaining a constant high pressure inside the cell, and a limited electrochemical stability window. , A cubic aluminum-doped Li 7 La 3 Zr 2 O 12 (LLZO) garnet-type solid electrolyte has one of the highest ionic conductivities . NASICON-type solid electrolytes like Li 1+ x A 1 x Ti 2– x (PO 4 ) 3 (where x = 0.3) (LATP) have high oxidative stability and, thus, are compatible with high-voltage-positive electrode materials and are stable under ambient conditions. − Similarly, perovskite-type ISEs such as Li 3/8 Sr 7/16 Ta 3/4 Hf 1/4 O 3 (LSTH) are known to be stable under ambient conditions and have high room-temperature conductivity and low interfacial resistance …”

Core–Shell NaBH4@Na2B12H12 Nanoparticles as Fast Ionic Conductors for Sodium-Ion Batteries

“…On the other hand, closo-type complex hydride-based electrolytes can exhibit a very high ionic conductivity. 14,15 Notably, Na 2 B 12 H 12 has been reported to display a superior Na + conductivity of 10 −1 S cm −1 at a temperature of 256 °C upon phase transition from its monoclinic to disorder body-centered cubic phase. 25−28 Approaches of anion "mixing" have also been reported to lead to a significant improvement in the ionic conductivity of Na 2 B 12 H 12 .…”

“…Among the current solid-state sodium electrolytes, extensive studies have been performed on the crystalline oxide electrolytes including β-alumina and NASICON. − The ionic conductivity of these oxide electrolytes can reach 10 –3 S cm –1 at room temperature, but their practical application is still limited by the instability of the Na metal electrode/oxide electrolyte interface. The latter also displays a high resistance of 1600 Ω cm 2 at 25 °C. , Alternative sulfide glass-ceramic-based Na-ion conductors have also been widely explored .…”